Real Rate of Return Calculator
Calculate your inflation-adjusted real rate of return.
What this calculator does
Nominal returns tell you how many more pounds you hold. The real rate of return tells you whether those pounds buy more than they did, which is the question that actually decides whether you are better off. It uses the Fisher equation: one plus nominal, over one plus inflation, minus one.
Enter the starting value, the current value, and the number of years, and the calculator gives you the gain, the return percentage, and an annualised rate. Set that annualised rate against CPI over the same period and you have an honest reading of what happened to your purchasing power.
When to use it
Use real returns whenever the horizon is long enough for inflation to compound — pension projections, school fee planning, a gilt ladder, or comparing performance across different decades. A 12 percent return during the 1970s, when UK inflation ran into double digits, was a substantial loss in real terms.
It is also the right way to look at cash. Money in a current account earning nothing while CPI runs at 4 percent is not standing still; it is shrinking at a measurable rate, and seeing that expressed as a negative percentage tends to prompt the move to a decent savings rate or an ISA.
Understanding the inputs
Enter the starting and ending values in nominal pounds — the actual figures on your statements, not adjusted ones. The calculator returns the nominal annualised rate, which is the input the Fisher adjustment needs.
Years should be the actual span and takes decimals. To convert to a real rate, apply the Fisher formula to the annualised figure using average CPI over the same period, which the ONS publishes monthly. For forward-looking plans, the Bank of England's 2 percent target is a starting point, though recent years have run well above it.
How is this calculated?
Real Rate = (1 + Nominal) / (1 + Inflation) − 1. Approximation: Real ≈ Nominal − Inflation.
A worked example
Suppose a portfolio returned 5.6 percent a year across a period when CPI averaged 2.8 percent. Subtraction suggests 2.8 percent real. The Fisher equation gives 1.056 divided by 1.028, minus one, which is 2.72 percent.
Applied to £100,000 over twenty-five years, the nominal balance grows to roughly £390,000. In today's money that is about £196,000 — barely a doubling in purchasing power despite a near quadrupling of the number on the statement. The gap between those two figures is what inflation quietly took.
Limitations and assumptions
The calculator assumes one flat return and one flat inflation rate for the entire period. Both move considerably year to year, and the order in which they arrive matters for anyone contributing or drawing down. Past returns and past inflation do not predict future ones.
It also ignores tax, which HMRC charges on nominal rather than real gains and which therefore erodes real returns further, and it assumes headline CPI matches your own spending pattern, which it rarely does exactly. Nothing here is investment advice or a personal recommendation.
Common Questions
- What is the real rate of return?
- It is your return once inflation is removed — what your money gained in buying power rather than in pounds. The precise calculation is one plus the nominal return divided by one plus inflation, minus one. Simply subtracting inflation gives a close approximation that becomes inaccurate as rates climb.
- Why not just subtract inflation?
- You can, but the shortcut flatters you as rates rise. At 5 percent nominal and 3 percent inflation, subtraction says 2 percent while the Fisher equation gives 1.94 — trivial. At 15 percent nominal and 10 percent inflation, subtraction says 5 percent but the true real return is 4.55 percent.
- Should I use CPI or RPI?
- CPI is the ONS headline measure and the basis for the Bank of England's 2 percent target, most benefit uprating, and the state pension triple lock calculation. RPI runs persistently higher and is being aligned with CPIH. For personal planning, CPI is the sensible default, though your own inflation rate may differ.
- Can my real return be negative when the nominal return is positive?
- Very often, and this is exactly what the measure exists to expose. A savings account paying 3 percent while CPI runs at 5 percent loses roughly 1.9 percent of purchasing power a year. UK savers spent much of the past fifteen years in precisely this position without it appearing on any statement.
- What real return have UK assets delivered historically?
- Long-run studies of UK equities put the real return at roughly 5 percent a year over more than a century, with gilts substantially lower and cash close to zero after inflation. These are averages across enormous variation, not promises, and any particular decade can look nothing like the long-run figure.
- How does tax affect my real return?
- It compounds the damage, because HMRC taxes nominal gains rather than real ones. Earn 5 percent nominal, pay dividend or savings tax on it, and face 3 percent inflation, and a positive-looking return can become negative in real terms. This is a strong argument for using ISA and pension allowances first.
- Do index-linked gilts protect against inflation?
- They are designed to. Index-linked gilts uprate principal and coupons in line with inflation, delivering a contracted real yield. That removes inflation risk but not duration risk — long-dated linkers fell dramatically in 2022 when real yields rose, so they are not a safe haven in the short term.
- Does the real return matter inside an ISA?
- Just as much. An ISA removes tax but does nothing about inflation. Cash held in a Cash ISA paying below the inflation rate loses purchasing power exactly as taxable cash does. The tax shelter improves your nominal return; only investment return above inflation improves your real position.
- How should I use real returns in retirement planning?
- Work entirely in today's money. Over a 30-year retirement, 3 percent inflation multiplies the cash cost of the same lifestyle by roughly two and a half. Projecting in nominal terms makes a pot look far more robust than it is; projecting in real terms keeps the plan honest about what it must actually fund.