Index-Linked Gilt Calculator (Linkers)

An index-linked gilt, or "linker", is a UK government bond whose coupon and principal both rise with an inflation index, so the cash you get back keeps pace with the cost of living rather than being eroded by it. Its return is built from two parts that compound together: an inflation uplift applied to the principal, plus a "real yield" paid on top - roughly, total nominal return ≈ (1 + real yield) × (1 + inflation) − 1 over the holding period. That is the calculation an index linked gilt calculator performs for you, turning a real yield and an inflation assumption into the actual pounds you can expect at maturity.

This page explains how linkers work, how the maths is done, and when an inflation-linked gilt is the right home for your money instead of a conventional gilt or a savings account.

What does the index linked gilt calculator tell you?

An index linked gilt calculator takes the gilt's real yield, your chosen inflation assumption, and the years to maturity, then projects the inflation-adjusted principal you receive at redemption and the total nominal return along the way. Because a linker's coupon and final principal are both scaled up by an inflation index - historically the Retail Prices Index (RPI), with a planned move towards CPIH from 2030 under RPI reform - the calculator has to layer the inflation uplift on top of the real yield rather than treating them separately. The headline figure it produces is your expected nominal return, the number that lets you compare a linker fairly against a conventional gilt or a fixed savings rate.

• What linkers are: UK government bonds issued by HM Treasury through the Debt Management Office (DMO), whose coupon and principal both rise with an inflation index.
• The index used: historically RPI, with a planned transition towards CPIH from 2030 as part of RPI reform.
• Two-part return: an inflation uplift on the principal, plus a real yield paid on top - together they protect your buying power.
• Capital gains are CGT-free: for individuals, gains on gilts including linkers are exempt from Capital Gains Tax.
• The coupon is taxed: as savings income at your marginal rate for 2026/27 of 20%, 40% or 45%.
• Redemption value floats: a linker redeems with its inflation-adjusted principal at maturity, not a fixed £100.
• They can be volatile: if you sell a linker before maturity, its price can move sharply with real yields.

How is an inflation linked gilt return calculated?

The core idea is that a linker pays you a small, fixed real yield on a principal that itself grows with inflation. Suppose a linker offers a real yield of 1% and inflation runs at 3% a year. The principal is uplifted by 3% to preserve its buying power, and the 1% real yield sits on top of that, so the approximate total nominal return for the year is (1 + 0.01) × (1 + 0.03) − 1 = 4.03%. Compound that over the years you hold the gilt and you get the projected redemption value the calculator reports.

This is why a linker is fundamentally different from a conventional gilt. A conventional gilt pays a fixed coupon and redeems at a fixed £100, so high inflation quietly destroys its real value. A linker's principal moves with the inflation index, so the buying power of your capital is protected by design. The trade-off is that you accept a lower, known real yield in exchange for handing the inflation risk to the government. If you want to model the inflation side on its own first, the inflation calculator shows how a given rate erodes a fixed sum over time, which is exactly the erosion a linker is built to neutralise.

Nominal value at maturity under different inflation assumptions

The table below shows the approximate nominal value at maturity of a £10,000 linker bought with a 1% real yield, held for 10 years, under four inflation scenarios. It uses the compounding rule (1 + real yield) × (1 + inflation) − 1 applied each year. The point to notice is how much the final figure swings with the inflation assumption - which is precisely why an index linked gilt calculator asks you to choose one.

Read across the rows and the lesson is clear: the higher inflation turns out to be, the better the linker performs in nominal terms, because the inflation uplift is doing most of the heavy lifting. In real terms, though, you keep the same modest 1% above inflation in every scenario - that is the whole promise of a linker. The figures are approximate and assume coupons are reinvested at the same real yield; your actual outcome depends on the gilt's exact terms and the inflation path that occurs.

What is breakeven inflation and why does it matter?

Breakeven inflation is the single most important number when deciding between a linker and a conventional gilt of the same maturity. It is the gap between the conventional gilt's yield and the linker's real yield - the rate of inflation at which the two investments deliver the same return. If a conventional 10-year gilt yields 4.2% and the equivalent linker has a real yield of 1%, the breakeven inflation is roughly 3.2%.

The rule is simple: if you expect average inflation over the holding period to be above the breakeven rate, the linker wins; if you expect it to be below, the conventional gilt wins. Buying a linker is therefore a bet that inflation will be higher than the market is currently pricing in. Above breakeven the inflation linked gilt protects and rewards you; below it you would have been better off locking in the fixed yield. The gilt yield calculator gives you the conventional gilt's after-tax yield to set against the linker, and the gilt vs savings calculator shows how both stack up against a fixed bank rate.

How the index-linked gilt calculator works

Behind the scenes, the calculator follows the same steps a bond desk would, just instantly:

• Step 1 - Take the real yield. It starts with the linker's quoted real yield, the fixed return you earn above inflation if you hold to maturity.
• Step 2 - Apply your inflation assumption. It uplifts the principal each year by your chosen inflation rate, mirroring how the inflation index ratchets up the gilt's coupon and redemption value.
• Step 3 - Compound the two together. It combines them with (1 + real yield) × (1 + inflation) − 1 for each year and compounds over the full holding period to project the inflation-adjusted principal at maturity.
• Step 4 - Tax the coupon, not the gain. It taxes only the coupon as savings income at your 2026/27 marginal rate of 20%, 40% or 45%, while leaving the capital gain free of Capital Gains Tax, then reports your net nominal return.

The result is a like-for-like figure you can compare against a conventional gilt, a fixed-rate bond or a savings account. Because the coupon on a low-real-yield linker is small, most of the return arrives as the CGT-free uplift in principal - a tax profile similar to a low-coupon conventional gilt, which the savings interest tax calculator can help you weigh against taxable bank interest.

When linkers make sense

An inflation-linked gilt is not always the right choice; it is a specific tool for a specific worry. Here is when reaching for a linker is the sensible move:

• You expect inflation above breakeven. If your honest view is that inflation will run hotter than the market-implied breakeven rate, the linker is the better bet. If you think inflation will undershoot, take the conventional gilt's higher fixed yield instead.
• You are protecting long-dated, real spending. Linkers suit money earmarked for liabilities that themselves rise with prices - retirement income, school fees, future care costs. Matching a linker's maturity to when you will spend the money locks in the real return.
• You can hold to maturity. Linkers can be volatile if sold early, because their price swings with real yields. Only the inflation-adjusted principal at redemption is guaranteed, so buy with the intention of holding the full term.
• You have used your tax wrappers. Inside an ISA or SIPP both the coupon and the uplift are tax-free, removing any tax drag. If you have allowance spare, check the ISA calculator before buying linkers in a taxable account.
• You want certainty of buying power, not certainty of pounds. A linker fixes your real return and lets the nominal figure float; a conventional gilt does the reverse. Choose the one whose certainty matches what you actually care about.

You can confirm exactly how linkers are issued and redeemed at the UK Debt Management Office, and read the official position on the CGT exemption for gilts in the GOV.UK Capital Gains Tax guidance, which lists gilts among the assets you do not pay CGT on.

Who benefits most from holding linkers?

Linkers earn their keep for investors with long horizons and a genuine fear of inflation eating their capital. A retiree drawing income over twenty or thirty years, a parent saving towards fees that rise every September, or anyone holding a large cash buffer they cannot afford to see debased - these are the natural buyers of an inflation linked gilt. For them, the certainty that the principal will keep pace with prices is worth more than the slightly higher fixed yield a conventional gilt might offer today.

For shorter horizons, or where you actively expect inflation to fall below breakeven, a conventional gilt or a fixed savings rate usually wins. The honest answer comes from running your own numbers: feed a real yield and your inflation view into the index linked gilt calculator, compare the projected nominal return against the conventional gilt's yield and the breakeven rate, and let the comparison decide. That is the entire purpose of an index linked gilt calculator - it cuts through the two-part maths of real yields and inflation uplift and tells you, in one number, whether the linker protects your buying power better than the alternatives for someone in your position.

This is an estimate to help you compare options, not investment advice. A linker's actual return depends on the inflation path that occurs, the price you pay and the date you sell or redeem; linkers can be volatile if sold before maturity. Tax treatment depends on your personal circumstances and may change.

Who should use this calculator

Index-linked gilts have both coupon and redemption value uprated by inflation, so they protect the real value of capital in a way conventional gilts and cash cannot. This projects the outcome from a real yield and an inflation assumption.

The concept to grasp is the real yield: the return above inflation. When real yields are negative — as they were for much of the 2010s — you are guaranteed to lose purchasing power by holding to maturity, even though the nominal figure grows. A positive real yield is what makes a linker worth owning.

What this calculator assumes

• Coupon and redemption value are uprated by RPI under the standard UK linker structure.
• The real yield entered is the return above inflation; nominal return is real yield plus actual inflation.
• The inflation assumption is applied evenly across the term.
• The linker is kept until it redeems.

Limitations — what it does not cover

• The indexation lag, typically three months, meaning uprating trails actual inflation.
• RPI reform, aligning RPI with CPIH from 2030, which reduces expected uprating for longer-dated linkers.
• Price volatility. Long-dated linkers are highly sensitive to real yield movements — some fell over 50% in 2022.
• Tax — the coupon is taxable, though the capital uplift remains CGT-free.
• Deflation, where uprating can work against you.
• Your personal inflation rate, which may differ from RPI.