Index-Linked Gilts Explained: How UK Inflation-Protected Government Bonds Work

Index-linked gilts adjust both coupon payments and principal repayment in line with the Retail Prices Index (RPI). That single design choice separates them from every other fixed-income instrument available to UK investors.

Take the 0⅛% Index-linked Treasury Gilt 2036. The 0.125% coupon looks absurd next to a conventional 10-year gilt yielding 5.07%. But that coupon is a real yield — it sits on top of whatever RPI accrues between issue and payment. The 2036 linker's clean price today is £85.34 but its dirty price is £134.44 — that £49 gap is the cumulative inflation uplift on principal since the gilt was issued in 2013. You pay the dirty price; you get the inflation-uplifted principal back at maturity.

The indexation uses an 8-month lag for gilts issued before 2005 and a 3-month lag for newer issues. Payments don't respond instantly to inflation spikes. During the 2022-23 energy crisis, holders waited months for the uplift to feed through. The same lag applies now — the Iran-driven energy shock that began at the end of February 2026 won't fully reach gilt coupon calculations until the autumn.

Linkers index to RPI — not CPI or CPIH. According to the latest ONS bulletin (released 22 April, next print due 20 May), RPI ran at 4.1% in March 2026 against CPI at 3.3% — a 0.8 percentage point gap, wider than February's 0.6. That spread compounds significantly over a 20- or 30-year gilt. It also means linkers provide more inflation protection than headline CPI suggests. The gap widens whenever motor fuels, council tax, or mortgage interest spike (RPI weights these more heavily) — which is exactly what happened in March, when petrol jumped 8.6 pence per litre and diesel 17.6 pence on Iran-driven supply disruption.

For most of the 2010s, index-linked gilt real yields were negative. You were paying the government for the privilege of inflation protection. That era is over — and the curve has steepened materially since the 30 April refresh.

Real yields from the UK index-linked gilt market on 12 May 2026:

The 10-year benchmark sits at 1.65% real — up 14bps from 1.51% on 30 April. The full curve has steepened roughly 10-15bps in two weeks. Buy today, hold the 2036 to maturity, and you earn RPI inflation plus 1.65% annually — regardless of what happens to energy prices, Bank Rate, or geopolitics.

What drove this? Two things working in the same direction. The Bank of England cut Bank Rate from 5.25% to 3.75% between August 2023 and December 2025, then stopped — and the Iran conflict has frozen further cuts. Markets are now pricing in hikes later in 2026 if inflation keeps printing hot. Second, the IMF's downgrade to UK growth means more borrowing, more gilt supply, and term premium creeping back into the long end. The full meeting-by-meeting take is in our BoE rate-cycle developing story.

A real yield of 1.65% compounding over 10 years adds roughly 18% to your purchasing power beyond inflation. From a risk-free asset, that is genuine wealth-building territory.

The breakeven inflation rate tells you which gilt wins versus a conventional. With conventional 10-year gilts at 5.07% and the 2036 linker at 1.65% real, the implied breakeven is 3.42%. If RPI averages above 3.42% over the next decade, linkers win. Below it, conventional gilts win. RPI sat at 4.1% in March.

The more useful comparison for most readers is cash ISA vs linker. Take £20,000 — the full ISA allowance — and assume a 10-year horizon.

Option A: best cash ISA at 4.65% AER fixed, tax-free in the wrapper.

• Nominal value after 10 years: £20,000 × 1.0465¹⁰ = £31,478
• If RPI averages 3.5%, real value = £31,478 / 1.035¹⁰ = £22,326 in today's money — a real gain of £2,326 over the decade.
• If RPI averages 4% (closer to today's reading), real value drops to £21,289.
• If RPI averages 4.5%, real value drops to £20,275 — a real gain of just £275 over ten years on £20,000.

Option B: 10-year index-linked gilt at 1.65% real, held in the same ISA wrapper.

• Real value after 10 years (guaranteed): £20,000 × 1.0165¹⁰ = £23,556 in today's money
• This number does not change if RPI is 2%, 4%, or 8%. The real return is locked.

The crossover. At 4.65% nominal vs 1.65% real, the cash ISA wins only if RPI averages below ~2.95% over the decade. RPI has not been below 2.95% on a sustained basis since 2021. The Bank's own February forecasts didn't see CPI returning sustainably to 2% before late 2027, and that was before Iran. RPI runs structurally 0.5-0.8 percentage points higher than CPI thanks to the formula effect. You don't have to be an inflation hawk to think average RPI above 2.95% for a decade is the central case.

For a live cash ISA comparison, see our cash ISA comparison tool. For the deeper trade-off between locked-in linkers and flexible cash, see our comparing UK savings accounts ISAs and gilts guide.

Tax treatment favours linkers for higher-rate taxpayers held outside an ISA. All gilts are exempt from capital gains tax, and the inflation uplift on principal counts as capital gain, not income. Only the (tiny) real coupon is taxed as income. Hold in an ISA or SIPP and even that disappears.

Picking the right point on the curve matters more than picking linkers in the first place. Two real choices, both £10,000 invested today.

Choice A: 0⅛% IL Treasury Gilt 2028 (T28). Two years and three months to maturity, real yield -0.23%. Clean £100.81, dirty £147.83. £10,000 nominal costs £14,783 to acquire. You earn RPI inflation minus 0.23% per year. With RPI at 4.1%, nominal return is around 3.87% — but lock that in and you cap your exposure to the next two CPI prints, no more.

Choice B: 0⅛% IL Treasury Gilt 2036 (TG36). 10 years 196 days to maturity, real yield +1.65%. Clean £85.34, dirty £134.44. £10,000 nominal costs £13,444 to acquire. You earn RPI inflation plus 1.65% per year for a decade.

Simulate three RPI scenarios:

The shorter linker only beats the longer one if you can roll the proceeds in 2028 into something paying more than today's 1.65% real. That requires real yields to rise further. They might — but you are now making an active call on real-rate direction rather than locking in a guaranteed real return. The 2036 buyer outsources that call to the market and pockets 1.65% real for ten years.

The price-volatility caveat. TG36 trades at £85.34 clean. If 10-year real yields rise another 50bps, that price falls roughly £4.50. Hold to maturity and you receive the inflation-uplifted £100 nominal regardless — but you must stomach the mark-to-market. Long-dated linkers are far worse: TG56 trades around £52, and the 2068 issue around £45. Only buy them if you can hold or accept severe mark-to-market swings. See why gilts can hammer your capital for the worked downside.

For the full curve breakdown and how the 10-year benchmark interacts with mortgage and savings rates, see our gilt yields explained — the GiltEdge page that drives the most search traffic and the natural companion to this guide.

Three routes to index-linked gilt exposure, each with different trade-offs.

Individual gilts via a broker. Hargreaves Lansdown, AJ Bell, interactive investor, and most UK stockbrokers let you buy specific index-linked gilts on the secondary market. You choose the maturity, lock in the real yield, and hold to redemption. Dealing fees run £5-12 per trade. The dirty price is what shows up on your contract note: TG36 will charge you around £134 per £100 nominal even though the clean price quoted is £85. The difference is accumulated inflation since 2013 — you are not overpaying.

The DMO Purchase and Sale Service. The UK Debt Management Office, administered by Computershare, allows approved investors to buy gilts directly. Slower and less convenient than a platform, but viable for buy-and-hold investors. For step-by-step instructions, see our practical gilt buying guide.

Index-linked gilt funds and ETFs. The iShares UK Index Linked Gilts ETF and Vanguard UK Inflation-Linked Gilt Index Fund provide diversified exposure across maturities. Simplicity and liquidity are the upside. The downside: no maturity date. A fund holds a rolling portfolio, so you never lock in a real yield — you are always exposed to changing real rates. Fund investors have suffered capital losses since 2022 even while underlying inflation protection worked as designed.

Tax wrappers matter. Gilts fit inside a Stocks & Shares ISA or SIPP. The CGT exemption already covers the inflation uplift on principal, so the main wrapper benefit is sheltering the income. For a 40% taxpayer holding £50,000 nominal of linkers outside a wrapper, the annual tax drag is modest — a few pounds on those tiny coupons — but it compounds over decades. Check our investing hub and gilts hub for platform fee comparisons and live yield data.

Minimum investment is as low as one penny nominal, though platforms set practical minimums around £100.

The 10-year nominal gilt yield trajectory tells the macro story:

From a sub-4.50% trough in February to 5.07% today is a 60bps move in ten weeks. The Iran shock did most of the work. The Strait of Hormuz closure on 2 March 2026 triggered the largest energy supply disruption in recorded history. Brent crude touched $126 by late April, QatarEnergy declared force majeure, and UK gilt yields spiked harder than any other G7 economy's borrowing costs. Domestic heating oil prices were up 95.3% year-on-year — the highest since September 2022.

For index-linked gilt investors, this cuts both ways. Higher inflation expectations make the protection more valuable — RPI has already moved from 3.6% in February to 4.1% in March, and energy costs are still feeding through. Buying now, you are getting a much better deal than six months ago. If you already own long-dated linkers, you have felt the pain in mark-to-market terms — but the inflation protection mechanism has worked as designed.

For the BoE's reaction, see our analysis of how the Iran conflict killed the rate-cut cycle.

Three things to watch over the next quarter:

1. The May 2026 ONS print (due 20 May). RPI moved from 3.6% to 4.1% in one month. Another step up will pull real yields higher and make breakeven inflation cross above 3.5% — at which point even moderate inflation hawks should re-price the cash-vs-linker decision.

2. The June MPC meeting. Markets are split between hold and a token 25bp hike. A hike would push nominal yields higher and could nudge real yields above 1.75% on the 10-year — a level not seen since 2008.

3. RPI reform in February 2030. The government has confirmed RPI aligns with CPIH from that date. For linkers maturing before 2030 — T27, T28, T29 — irrelevant. For anything longer, your inflation measure switches from RPI (4.1% in March) to CPIH (3.4%) — a permanent reduction in the uplift of roughly 0.4-0.8 percentage points annually. The Supreme Court confirmed in 2022 that the government has legal authority to make this change. Price the reform into any gilt maturing after 2030: the actual uplift on TG36 will be RPI-style for years 1-4 and CPIH-style for years 5-10. Today's quoted real yield assumes RPI throughout, so the realised real return will be lower than the headline number suggests.

Buy if: You are within 10-15 years of retirement and want to guarantee your pot keeps pace with living costs. A ladder of linkers maturing in sequence gives you inflation-proofed income without equity risk. At today's 1.65% real on the 10-year, you are being paid handsomely for the protection. The debate between gilts vs savings accounts and the case against buying gilts is worth reading for both sides.

Buy if: You are a higher-rate or additional-rate taxpayer looking for tax-efficient fixed income. The CGT exemption on the inflation uplift makes linkers more efficient than corporate bonds or savings accounts where interest is fully taxed. Our savings hub compares after-tax alternatives.

Buy if: You genuinely believe inflation will stay elevated. With geopolitical conflict, energy disruption, and fiscal pressures, the arguments for persistent above-target inflation are stronger than they have been since the 1970s. Gold has outperformed everything in 2026 — but linkers give you the inflation hedge with zero credit risk and a guaranteed maturity value.

Don't buy if: You might need the money before maturity. Index-linked gilt prices swing violently — TG56 trades around £52, the 2068 issue around £45, both well below par. Selling early in a rising-rate environment crystallises real losses.

Don't buy if: You think inflation will collapse to 1-2% and stay there. In that scenario, conventional gilts at 5.07% will massively outperform, and you will have locked in 1.65% real when you could have had 3%+ nominal above actual inflation.

Don't buy if: You want simplicity. The RPI lag, the dirty/clean price distinction, and the 2030 reform make linkers genuinely complex. If that is off-putting, a diversified gilt fund handles the complexity for a small ongoing charge. For a broader look at bonds, see our how to buy bonds guide.

This article is for informational purposes only and does not constitute financial advice. You should seek independent financial advice before making any investment decisions.