giltsyield.com Help & User Guide

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

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. It is the standard measure for comparing bonds. On the site this is generally shown gross; a net (post-tax) yield can also be displayed.

Book yield

The return you locked in on the day you bought, rather than the one on offer today. It is fixed the moment you buy and only moves when you buy more. Market swings and selling leave it alone. For a ladder you mean to hold to maturity, this is the return you have contracted for.

Don't compare it with the price you paid, though. A gilt bought below £100 drifts up towards par simply because it is getting closer to being repaid, so paying less than it is worth today doesn't on its own mean you beat the market. Compare it with your book value instead.

Book value (amortised cost)

What your holding would be worth today if it had earned exactly the return you locked in. Your cost isn't static: a gilt bought at a discount climbs towards £100 and you earn that climb year by year, so we carry your cost forward at your own rate rather than leaving it at the price you paid.

That makes it the figure to hold today's price against. If today's price sits below it, the market is offering more than you locked in. If it sits above, you did better.

It leaves out accrued interest, and so does the cost shown beside it. That matters: accrued interest builds up between coupon dates and then resets to nothing when the coupon is paid, and if one figure carried it and the other did not, the swing would be larger than a whole year of the return you are trying to see. On the Book yield tab the accrued is printed under each figure, so you can always add it back.

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.

2. Getting around the site

The top navigation bar is the same on every page:

• [G] / Home: the landing page with featured and latest articles.
• Yield Curve: the fitted UK gilt (and RPI/inflation) yield curve for any date.
• Gilts (dropdown): Conventional Gilts, Inflation-Linked Gilts, and Post-Tax Yield.
• Holdings (dropdown): Portfolios, Cash Flow Analysis, Taxable Income, and Trades.
• Ladder: the bond ladder builder.
• Insights: AI-generated daily market insights.
• Assistant: ask for gilt data, portfolio answers and site help in plain English (login required).

There is also a Search box (press Ctrl+K / ⌘+K) to jump to any gilt by name, ticker or ISIN, a light / dark / auto theme toggle in the bottom-right, and a user menu (top-right) once you are logged in for Profile, Change Password and Logout.

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

1. Pick a date (any business day from 2023-01-01 to today) and press Go to see the curve on that day.
2. Switch between the gilt curve and the RPI / inflation curve.
3. For the gilt curve you can view the par curve or the zero-coupon (zc) curve.
4. 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:

Using the pricer to check a price or yield

1. Open a gilt (from Gilts → Conventional Gilts or via search) and choose a valuation date (2023-01-01 to today).
2. The page pre-fills current market clean price, dirty price, accrued interest and (ILG) index ratio.
3. To see the yield implied by a different price, use the dirty_price parameter 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

1. Go to Portfolios → add (or you'll be prompted if you have none).
2. Give it a name (3–50 characters).
3. Optionally set a portfolio-specific tax rate (0/20/22/40/42/45/47/48 or "Inherit from profile") and settlement delay (T+1/T+2 or inherit). Leaving these on "Inherit" uses your profile defaults.
4. 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 showing 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 five tabs over it. Four of them list the same holdings in the same order and change only which figures are shown, so you never have to scroll sideways to find a column:

• Summary: quantity, allocation, market value, market yield, book yield and total gain/loss.
• Profit & loss: market value against cost basis, split into unrealised, realised and income.
• Book yield: one line per holding that you can open up. See below.
• Pricing: quantity, then the prices per £100 (what you paid on average, your book price, and today's clean and dirty prices), then the amounts those prices produce. The row adds up as you read it: clean amount plus accrued interest is market value. (For an index-linked gilt the quoted price is before inflation uplift while the amounts are after it, so the two won't tie by multiplication. The amounts are the ones to trust.)
• Risk & carry: allocation, market 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.

Holdings you have sold or seen mature

A gilt you sold in full, or held until it was repaid, keeps its place in the table. It has no market value left, so rather than sitting among your live holdings it goes into a folded group just above the total. The fold tells you how many there are and what they contributed, and opening it shows each one. What you made on them, and the coupons they paid along the way, still count in your totals, so the rows and the total always agree.

Seeing where your book yield comes from

The Book yield tab shows where that figure comes from. Each holding is one line showing what it cost, what it is worth today, and the return you locked in. Open a line and you see every purchase behind it: when you bought, what you paid, and the return that particular purchase locked in.

The bottom row of each breakdown is the position as a whole. It is not the average of the purchases above it, and that is on purpose: each one is carried forward at its own rate, the amounts are added up, and the return is worked out once against that total. Averaging the rates would flatter it.

Accrued interest is left out of every money column here and printed underneath instead, so the columns can be read against each other. Cost is what you paid, Book value is what that has grown to at the rate you locked in, and Market value is what it is worth today. This is also why Cost here is a little lower than the Cost basis on the Profit & loss tab: that one is the full cash that left your account, accrued interest included.

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

1. Go to Holdings → Trades → add, or use the book trade form on any gilt's pricer page.
2. Select the portfolio, the gilt, and Buy or Sell.
3. Enter the trade date (must be on/after the bond's issue date), quantity (nominal), and price.
4. 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.
5. 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 either price (dirty) or clean_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

1. Select a UK tax year (6 April – 5 April).
2. Optionally filter by portfolio group to exclude ISA/SIPP holdings (where interest isn't taxable).
3. 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.
4. 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, and 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. Assistant (AI chat)

The Assistant answers questions in plain English instead of making you browse tables. Type a question; it works out the right query, fetches the data and replies in readable form, often with a chart. It can also read your own portfolio and explain how the site works, and 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, and 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>/: book yield per position; add lots=true for 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; optional inflation=<pct> to project index-linked gilt flows forward (0 / omitted keeps the current index ratio).
• /api/portfolio/taxable-income/: taxable-income CSV; optional tax_year=YYYY/YYYY and group params.
• /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 clear the bot check. 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 (0/20/22/40/42/45/47/48) 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.

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, which suits 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