How Inflation Destroys Investment Returns (And What To Do About It)

The number your broker never shows you

Your investment platform shows you a return of 8%. Your portfolio went up. You feel good. But there's a number your broker almost never shows you: the real return — what your money can actually buy after accounting for inflation.

At 3% inflation, an 8% return means a real return of approximately 5%. Over 30 years, the difference between these two figures is enormous. This guide explains exactly how it works and what to do about it.

The Fisher equation

The precise formula for real return is the Fisher equation:

For most practical purposes, the simpler approximation is good enough:

The difference only becomes meaningful at high inflation rates (above 10%).

What 3% inflation does to your money over time

At 3% annual inflation — the UK and US long-run average — purchasing power erodes steadily:

• After 10 years: £100 buys what £74 buys today
• After 20 years: £100 buys what £55 buys today
• After 30 years: £100 buys what £41 buys today

This means a pension pot of £500,000 in 30 years is only worth £205,000 in today's money at 3% inflation. The nominal number feels impressive; the real number is what matters for retirement planning.

Historical real returns by asset class

Over the long run (20+ year periods), the real returns of major asset classes have historically been:

• Global equities (MSCI World): +5 to +7% real per year
• US equities (S&P 500): +6 to +8% real per year
• UK equities (FTSE All-Share): +4 to +6% real per year
• Government bonds: +0 to +2% real per year
• Cash/savings accounts: −1 to +1% real per year (often negative in practice)
• UK residential property: +2 to +4% real per year (varies enormously by region)

The Rule of 72 — and the Rule of 115

The Rule of 72 tells you how long it takes to double your money at a given return rate: divide 72 by the annual return. At 6% real return, your money doubles in 12 years.

The Rule of 115 tells you how long it takes to triple your money: divide 115 by the annual return. At 6%, it triples in about 19 years.

These rules work for both nominal and real returns. Use the real return rule to understand what your money will actually buy, not just what it will nominally be worth.

How to beat inflation with your investments

• Own equities: Companies can raise prices, so equity returns tend to track above inflation over the long run. A globally diversified index fund is the simplest inflation hedge for most investors.
• Inflation-linked bonds: UK Index-Linked Gilts and US TIPS are explicitly linked to CPI. They guarantee a real return (often small or even negative) but provide certainty.
• Property: Real assets with rental income tend to track inflation. However, the illiquidity and leverage costs offset much of this benefit.
• Commodities: Gold and commodities have historically stored value over very long periods but have high short-term volatility and no income yield.
• Avoid excess cash: Cash in a savings account earning below the inflation rate is losing real value every year. Hold only your emergency fund in cash.

Monthly contributions vs lump sum

Investing a fixed amount monthly (pound-cost averaging) versus a single lump sum has been studied extensively. The evidence shows:

• If you already have the lump sum, investing it immediately beats spreading it over time about two thirds of the time — because markets trend upward over time.
• If you receive money regularly (salary), monthly investing is optimal and automatic.
• Monthly investing significantly reduces the risk of investing everything at a market peak.

Our calculator models both: set your monthly contribution alongside your initial investment to see the compounding effect of regular saving.