giltsyield.com — Complete Help & User Guide
Everything you can do on giltsyield.com: how to track UK gilt prices and yields, price bonds, build bond ladders, monitor a portfolio's profit & loss, understand the tax impact of your holdings, query market data in plain English, and access the data programmatically through the API.
giltsyield.com is a free tool for tracking UK government bonds (gilts). It provides live and historical prices and yields, fitted yield curves, portfolio analytics, tax reporting and an AI data-query assistant. It is an information tool only — nothing on the site is financial, investment or tax advice.
1. Gilts basics & terminology
Gilts are bonds issued by the UK government — effectively loans to HM Treasury. You receive regular interest payments (coupons) and, at maturity, the bond's face value (par, £100 nominal) is repaid. Gilts are considered low-risk and are widely used for stable income and portfolio diversification.
The two types of gilt on the site
Conventional gilts
Pay a fixed coupon, split into two equal payments per year, and repay £100 at maturity. Listed under Gilts → Conventional Gilts.
Index-linked gilts (ILGs)
Coupons and principal are scaled by an index ratio derived from the Retail Prices Index (RPI), protecting purchasing power against inflation. Listed under Gilts → Inflation-Linked Gilts.
Key terms used throughout the site
- Coupon
- The bond's annual interest rate on £100 nominal. Gilts pay it in two half-yearly instalments.
- Maturity date
- The date the £100 principal is repaid and the bond stops trading.
- Clean price
- The quoted market price of the bond, excluding accrued interest.
- Dirty price
- The price you actually pay = clean price + accrued interest (× index ratio for ILGs). This is the cash consideration per £100 nominal.
- Accrued interest
- The share of the next coupon that has built up since the last coupon date, paid by the buyer to the seller. It turns negative during the ex-dividend period (see the methodology section).
- Yield to maturity (YTM)
- The single annualised return that discounts all remaining cash flows back to today's dirty price — the standard measure to compare bonds. On the site this is generally shown gross; a net (post-tax) yield can also be displayed.
- Yield on cost
- The yield your cost locked in, as opposed to the yield on offer today: the rate that discounts a position's remaining cash flows back to what you actually paid for it. It is fixed at the moment you buy and moves only when you buy more — not when the market moves. For a ladder you intend to hold to maturity, this is the return you have contracted for, and the gap between it and the market yield tells you how the position has re-priced since.
- Index ratio (ILGs only)
- RPI at settlement ÷ RPI at issue. Scales coupons and principal for inflation. Conventional gilts always have an index ratio of 1.0.
- Modified duration / DV01
- Interest-rate sensitivity. Modified duration is the approximate % price fall for a +1% yield move; DV01 is the money change in value for a 1 basis-point move.
- Settlement (T+1 / T+2)
- The number of business days after the trade date on which cash and ownership change hands. Gilts conventionally settle T+1; the site lets you choose T+1 or T+2.
- Ticker
- The short code the site uses for each gilt (e.g. T26, T34). You can also search by name or ISIN.
3. The yield curve
The Yield Curve page plots the fitted term structure of gilt yields — the yield you would expect at each maturity from short-dated to ~50 years. Individual gilt quotes are shown as points around the fitted line so you can see which bonds trade rich or cheap versus the curve.
How to use it
- Pick a date (any business day from 2023-01-01 to today) and press Go to see the curve on that day.
- Switch between the gilt curve and the RPI / inflation curve.
- For the gilt curve you can view the par curve or the zero-coupon (zc) curve.
- Use Curve Attribution to compare the fitted curve between a start and end date and see how the whole term structure has shifted over a period.
Curves are fitted with the Nelson-Siegel-Svensson model — see the methodology reference for details.
4. Browsing gilts (yield tables)
Gilts → Conventional Gilts and Gilts → Inflation-Linked Gilts list every gilt currently in issue with its live price and yield analytics. Matured gilts are excluded automatically.
Controls at the top of the table
- Tax Rate (%) — choose 0, 20, 40 or 45. The table adds a net (post-tax) yield column computed for that rate, so higher-rate taxpayers can compare gilts on an after-tax basis.
- Settlement (T+1 / T+2) — changes the settlement date used for accrued interest and pricing.
If you are logged in, the table defaults to the tax rate and settlement saved in your profile (until you override them). Each row links through to that gilt's detail pages.
5. Bond detail pages & the pricer
Click any gilt to open its detail pages. Each gilt offers several views:
| View | What it shows |
|---|---|
| Pricer | Full price breakdown for a chosen date: clean price, dirty price, accrued interest & accrued days, gross & net yield, modified & Macaulay duration, previous / next coupon dates, ex-dividend date, settlement date, tenor bucket, and (for ILGs) index ratio, base RPI and implied RPI growth. From here you can also book a trade directly into a portfolio. |
| Cash flows | The full coupon & redemption schedule. Enter a number of units to scale the flows, and compare present values under mark-to-market, par-curve and (conventional) zero-coupon discounting. For index-linked gilts you can optionally enter an inflation assumption to project future flows forward (each flow then gets its own estimated index ratio); leaving it at 0 holds today's index ratio. |
| Yield curve | Plots the bond's yield and maturity against the fitted curve, so you can see the curve spread (how rich/cheap it is). |
| Historical | Historical price and yield over a date range you choose. |
| Attribution | Decomposes the price change between two dates into carry, roll-down, yield variation and an unexplained residual (see methodology). |
Using the pricer to check a price or yield
- Open a gilt (from Gilts → Conventional Gilts or via search) and choose a valuation date (2023-01-01 to today).
- The page pre-fills current market clean price, dirty price, accrued interest and (ILG) index ratio.
- To see the yield implied by a different price, use the
dirty_priceparameter on the bond price API (see API) or adjust the price when booking a trade.
6. Post-tax yield table & chart
Gilts → Post-Tax Yield ranks conventional gilts by their after-tax return. Because coupons are taxed as income but capital gains on gilts are tax-free (see taxation), low-coupon gilts are usually the most tax-efficient choice for higher-rate taxpayers holding gilts outside an ISA or SIPP. This page — and its chart view — make that trade-off visible so you can find the best net yield for your tax band.
7. Bond ladder builder
A bond ladder spreads money across gilts maturing in successive years. As each rung matures you get your principal back (and can reinvest it), giving predictable income, reduced interest-rate timing risk, and managed liquidity. The Ladder tool builds one for you automatically.
Two modes
- Income ladder — you specify a target annual income; the tool sizes each rung to deliver roughly that (inflation-adjusted) amount every year.
- Lump-sum ladder — you specify a total amount to invest; the tool allocates it across the rungs.
Inputs
- Ladder length — number of years/rungs (3 to 20).
- Target income — desired income per year (income mode).
- Inflation rate (%) — used to inflation-adjust the target income over time.
- Tax rate (%) — 0, 20 or 40; the tool picks the highest post-tax-yield gilt for each maturity year.
For each rung the builder shows the selected gilt, the amount to invest, the quantity to buy, its price and the resulting projected yearly cash flows. It chooses one bond per maturity year (the one with the best yield for your tax band) and works backwards from the final year, topping up any income shortfall.
8. Portfolios & holdings
Once logged in you can track real (or hypothetical) gilt holdings. Go to Holdings → Portfolios. You can hold up to 10 portfolios and 1,000 trades in total. (Email admin@giltsyield.com if you need more.)
Creating and managing portfolios
- Go to Portfolios → add (or you'll be prompted if you have none).
- Give it a name (3–50 characters).
- Optionally set a portfolio-specific tax rate (0/20/40/45 or "Inherit from profile") and settlement delay (T+1/T+2 or inherit). Leaving these on "Inherit" uses your profile defaults.
- Then book or import trades into it.
You can rename, edit settings for, or delete portfolios at any time. Deleting a portfolio removes its trades.
Portfolio groups
A portfolio group bundles several portfolios so you can view or report on them together — for example grouping all your ISA/SIPP portfolios, or by strategy. Create groups under Portfolio Groups → add (view them at Portfolio Groups), assign portfolios via checkboxes, and then filter the Portfolio and Taxable Income pages by group. Groups are especially useful to exclude tax-sheltered accounts from the taxable income report.
What the portfolio pages show
The Portfolios list gives you one row per portfolio — value, P/L, and the risk it carries (modified duration, DV01, daily carry) — plus a second table aggregating every gilt across all your portfolios, so a holding split between two accounts shows as one line.
Opening a portfolio gives you a single Positions table with one row per gilt and four tabs over it. Every tab lists the same holdings in the same order; the tabs change which figures are shown, so you never have to scroll sideways to find a column:
- Summary — quantity, allocation, market value, yield, yield on cost and total gain/loss.
- Profit & loss — market value against cost basis, split into unrealised, realised and income.
- Pricing — average price paid (AVP) and today's dirty price, then the clean amount and accrued interest that make up market value.
- Risk & carry — allocation, yield, modified duration, DV01, and what the position accrues and earns per day.
Any column can be sorted; the total row stays pinned at the bottom.
| Metric | Meaning |
|---|---|
| Market value | Current dirty-price value of each position and the total. |
| Allocation | Each position's share of total market value. |
| Unrealized P/L | Market value minus cost basis of open positions. |
| Realized P/L | Gains/losses locked in by sells and matured bonds, net of fees. |
| Income | Coupons and capital repayments you were entitled to receive. |
| Total P/L | Unrealized + realized + income. |
| Yield / Modified duration / DV01 | Value-weighted portfolio risk analytics. Duration is derived from the total DV01 rather than added up, since it is a weighted average and does not sum across holdings or portfolios. |
| Yield on cost | The yield the position's cost locked in, alongside the yield on offer today. Fixed when you buy; unaffected by later market moves or by selling. The portfolio figure is weighted by cost basis. |
| IRR | Money-weighted return (internal rate of return) across all cash flows plus today's value. |
| Daily accrued / daily carry | Interest accruing per day and daily return contribution. |
| Upcoming flows | A year-by-year matrix of the future coupons and redemptions you're entitled to, with an optional inflation assumption to project index-linked gilt flows forward. For a projection across all your portfolios, with tax-year / month grouping and a dated schedule, see Cash Flow Analysis. |
Historical performance
Each portfolio has a Historical view reporting performance over 1D, 1M, 3M, 6M, YTD and 1Y, using the Modified Dietz method (which adjusts for the timing of cash flows), plus a per-bond performance contribution breakdown.
9. Booking & importing trades
Booking a single trade
- Go to Holdings → Trades → add, or use the book trade form on any gilt's pricer page.
- Select the portfolio, the gilt, and Buy or Sell.
- Enter the trade date (must be on/after the bond's issue date), quantity (nominal), and price.
- The form pre-fills current market clean price, dirty price, accrued interest and (ILG) index ratio — adjust to match your contract note. You can also record brokerage fees.
- Save. The trade appears in the portfolio and feeds all analytics.
Quantity is the nominal amount (e.g. 1,000 = £1,000 face value). Prices are per £100 nominal. You can edit or delete any trade later from the Trades page.
Importing trades from a CSV
Go to Trades → import to upload many trades at once.
- Required columns:
date(YYYY-MM-DD),portfolio(must already exist),trade_type(Buy/Sell),ticker,quantity, and eitherprice(dirty) orclean_price. - Optional columns:
fees,accrued_interest,index_ratio. Anything you omit is computed for you from market data on the trade date. - Import mode: Append adds to existing trades; Replace wipes and re-loads all your trades.
10. Taxable Income report
Holdings → Taxable Income tells you, for a chosen UK tax year, exactly how much taxable interest to declare — so you don't have to reconcile contract notes and coupon statements by hand.
What it calculates
It produces three headline figures and a full audit trail:
- Coupons received (and accrued interest received on sells) — taxable income.
- Accrued interest paid on purchases — deductible under the Accrued Income Scheme.
- Net taxable income = coupons received − accrued interest paid.
Capital gains are excluded because gilts are exempt from Capital Gains Tax for UK individuals. The report correctly applies the Accrued Income Scheme: accrued interest paid when you buy reduces taxable income, and accrued interest you receive when you sell adds to it.
Two rules that are easy to get wrong
- Tax year attribution. A buy or sell's accrued-interest impact is attributed to the tax year of that security's next coupon date — not the trade's settlement date. A purchase settled just before 5 April, whose next coupon falls after 5 April, is correctly carried into the following tax year (shown with a Carried in marker in the report).
- No cross-security netting. A loss on one gilt only ever offsets interest on that same gilt — never a different one. The By Security breakdown flags any security where this produces an unrelieved loss for the year.
How to use it
- Select a UK tax year (6 April – 5 April).
- Optionally filter by portfolio group to exclude ISA/SIPP holdings (where interest isn't taxable).
- Read the headline totals for your tax return. The report is grouped by security — expand a security to see the individual trades and coupons behind its numbers, or use Expand all / Collapse all. A Pending marker just means a security's coupon for the year hasn't been paid yet; the amount is already fixed and is included in the totals as normal.
- You can download the full flat event list as a CSV (also available via the API).
11. Cash Flow Analysis
Holdings → Cash Flow Analysis projects the future coupons and redemptions across all your portfolios at once (or a chosen portfolio group), so you can see the shape of your income and principal returns over the years ahead.
Group by tax year, calendar year or month
Switch the whole view — chart, pivot and schedule — between UK tax year (6 Apr – 5 Apr), calendar year, or month. Toggling re-buckets instantly, without reloading the page.
Inflation assumption for index-linked gilts
Conventional gilt cash flows are contractually fixed. For index-linked gilts, only flows up to the latest published RPI are known; beyond that the page estimates them by growing RPI at the inflation assumption you enter (top-right). Raising it increases projected index-linked income. These future amounts are estimates — clearly marked as such — not contractual values.
Views & toggles
- Schedule (default) — each period with its total; click a period to expand the exact dated flows (date, bond, type, income, capital, total) inside it.
- Pivot — a bond × period grid with row/column totals and magnitude-shaded cells.
- Total / Income / Capital — combined flows, coupons only, or principal only.
- Nominal / Inflation Adjusted — Inflation Adjusted discounts every flow back to today's money at the same inflation rate, so you can compare future cash in real terms.
The page also shows summary tiles (total projected, coupon income, principal, next 12 months income, horizon), a stacked bar chart of income vs principal per period, and a CSV export of whichever view is active. Bond tickers link through to each gilt's pricer page. Like the other Holdings pages, when you are not logged in it shows a read-only demo portfolio.
12. GiltsQuery (AI assistant)
GiltsQuery lets you retrieve gilt data in plain English instead of browsing tables. Type a question; the assistant works out the right query, fetches the data and replies in readable form — often with a chart. It supports follow-up questions within a conversation. Login is required.
What it knows
- Quotes data — historical gilt prices and yields (from the start of 2023).
- Curves data — fitted historical yield-curve values for specific tenors.
- Your own portfolio — it can answer questions about your holdings and P/L. It only ever sees your data; each user's data is securely segregated.
Example questions
- "Plot the price of T34 over the past month."
- "What was the maximum price of T34 in 2024? On which date?"
- "What is the latest yield of T26 and what is its coupon?"
- "How did the 10-year yield change between April and May 2024?"
- "What is my portfolio P/L?"
Press Enter to send, Shift+Enter for a new line, and use New conversation to reset context. Data only goes back to the start of 2023, and answers are not guaranteed to be accurate — they are not a substitute for professional advice.
13. Market Insights
The Insights page publishes automatically-generated daily commentary on the gilt market. Insights are grouped by type:
- Trends — sustained moves in measures such as yields, the spread to the 2-year yield, trading volume or bid-ask spreads.
- Anomalies — unusual readings (e.g. abnormal volume) flagged against recent history.
- Changes — notable day-on-day price or yield moves.
Each insight includes a short explanation and a chart. You can browse insights for earlier dates. These are informational summaries, not recommendations.
14. API access
Every registered user has a personal API key for pulling their own portfolio data
programmatically or into a spreadsheet. Find your key and ready-made endpoint URLs on your portfolio's
API page (open a portfolio from
Holdings → Portfolios, then its API tab).
Authenticate by passing the key either as an X-API-Key header or an ?apikey=…
query parameter. Most endpoints return CSV by default; add ?format=json for JSON.
Endpoints (require your API key)
/api/portfolios/— list your portfolios./api/portfolio/pl/<portfolio>/— profit & loss./api/portfolio/book-yield/<portfolio>/— yield on cost per position; addlots=truefor the underlying purchase lots and the yield each one locked in./api/portfolio/trades/<portfolio>/— all trades./api/portfolio/flows/<portfolio>/— historical & current cash flows./api/portfolio/flows/upcoming/<portfolio>/— future entitled flows; optionalinflation=<pct>to project index-linked gilt flows forward (0 / omitted keeps the current index ratio)./api/portfolio/taxable-income/— taxable-income CSV; optionaltax_year=YYYY/YYYYandgroupparams./api/favorites/,/api/favorite/add/<ticker>/,/api/favorite/delete/<ticker>/— manage your favourite gilts.
15. Accounts & settings
- Register with an email and password (min 5 characters) and complete the captcha. You'll receive an activation email — click the link to confirm and log in.
- Log in with "remember me" if you like; there's a quick login modal too.
- Forgot password? Request a reset link by email (valid for 1 hour). For security the same confirmation message appears whether or not the email is registered.
- Change password from the user menu when logged in.
- Profile settings — set your default tax rate (0/20/40/45) and default settlement delay (T+1/T+2). These pre-fill the gilt tables, pricer and trade forms.
- Favourites — star gilts to keep them handy (managed via the API / search).
16. Methodology reference
This section explains how the numbers on the site are produced.
Yield curve fitting (Nelson-Siegel-Svensson)
Mark-to-market vs mark-to-model pricing
Accrued interest, ex-dividend & the coupon schedule
Index-linked gilts & the RPI index ratio
Yield, duration & DV01
Performance attribution (carry / roll-down / variation)
Portfolio P/L, cost basis, IRR & Modified Dietz
Yield on cost
A position's yield on cost is not the average of its lots' yields — present value is convex in yield, so averaging overstates it, by a basis point or so for lots bought close together and by ten or more once they are years apart. Instead each lot is valued at its own yield, the values are added, and the yield is re-solved against that total.
Sells relieve every open lot pro rata rather than oldest-first. This is what keeps the surviving cost equal to the average-cost basis used everywhere else on the site, so no P/L figure changes — and it means selling never moves your yield on cost, since every lot shrinks by the same proportion. Only buying moves it.
For index-linked gilts the figure is a real yield: cash flows are scaled by the index ratio at settlement and future inflation beyond the last published RPI is assumed to be zero, so the index ratio cancels between the flows and the price. A linker's yield on cost is therefore directly comparable with its market yield, but not with a conventional gilt's — and a portfolio total covering both is mixing real and money yields.
17. UK gilt taxation guide
General information for UK-tax-resident individuals holding gilts directly. Not tax advice — rules and allowances change and depend on your circumstances.
Capital gains are exempt
Gains on disposing of gilts — whether by selling or holding to redemption — are exempt from Capital Gains Tax for individuals, for both conventional and index-linked gilts. (This exemption applies to direct holdings; gilt funds follow ordinary fund rules.)
Coupons are taxed as savings income
Coupon interest is savings income, taxed at your marginal band, but sheltered by allowances:
- Personal Savings Allowance: £1,000 tax-free for basic-rate, £500 for higher-rate, £0 for additional-rate taxpayers.
- Starting rate for savings: up to £5,000 at 0% for those with low non-savings income.
The low-coupon strategy
Because gains are tax-free but coupons are taxable, low-coupon gilts convert more of your return into tax-free capital gain — attractive for higher-rate taxpayers. Demand can compress their yields, so use the Post-Tax Yield table to check the after-tax trade-off rather than assuming the low-coupon bond always wins.
Tax wrappers & index-linked gilts
- ISAs: interest is tax-free and there's no reporting requirement.
- SIPPs/pensions: tax relief on contributions, tax-free growth, and a 25% tax-free lump sum at retirement.
- Index-linked gilts: the RPI inflation uplift is tax-exempt, improving tax efficiency.
Use the Taxable Income report to total your declarable interest each tax year.
18. Where to buy gilts
giltsyield.com does not sell gilts — it's an analytics tool. You buy gilts through one of two routes:
- Secondary market via a stockbroker (most common) — platforms such as Hargreaves Lansdown, Interactive Investor, AJ Bell and others offer a wide choice of maturities and the flexibility to buy and sell existing gilts. Expect dealing fees and, on some platforms, minimum investments.
- Primary market via DMO auctions — the UK Debt Management Office issues new gilts at auction. Auctions are infrequent and involve competitive bidding, often with high minimums, so most retail investors use a broker.
Choose a broker on selection, fees and account minimums. Once you own gilts, record your trades on giltsyield.com to track P/L, income and tax.
19. Frequently asked questions
Do I need an account, and is it free?
Can I try the portfolio features before registering?
How current are the prices? Why doesn't a price match my broker exactly?
What's the difference between clean and dirty price, and which do I enter for a trade?
Why is my accrued interest negative?
What tax rate should I pick, and what does the net yield mean?
Are capital gains on gilts taxable? What do I actually declare?
How do I exclude my ISA/SIPP from the taxable income report?
How do I bulk-load my existing holdings?
What's the difference between IRR and the "performance" figures?
Are there limits on portfolios or trades?
Can GiltsQuery see other users' portfolios?
How far back does the data go?
I didn't get my activation or password-reset email — what now?
Where do I get my API key and how do I use it?
X-API-Key header or ?apikey=…
query parameter. Add ?format=json for JSON instead of CSV. Keep the key private.
Important disclaimer
This website and the information it contains are for informational purposes only. It is not a substitute for professional financial advice, investment recommendations, or other professional services. We do not guarantee the accuracy of the data or information presented.
Questions or suggestions? Email admin@giltsyield.com. See also our Privacy Policy.