What your money grows into.

Future value: the single question behind most financial planning

If I put £X aside today, or £Y per month, at some expected return, what will it be worth by date Z? That's the future-value question, and it sits underneath almost every long-horizon decision: pension contribution rate, savings goals, comparing investment products, deciding whether to overpay a mortgage or invest. The formula is straightforward; the judgment is in the assumptions.

The two formulas, separated cleanly

Future value of a lump sumFV = PV × (1 + r)ⁿ. You put in 10,000 today, leave it for 20 years at 6%, and end up with 32,071. Future value of a series of regular contributions (an annuity)FV = PMT × [((1 + r)ⁿ − 1) / r]. You contribute 300 monthly for 20 years at 6% and end up with 138,600. This tool handles both — don't confuse them when interpreting the result. A lump-sum answer doesn't include ongoing saving; an annuity answer assumes no starting pot.

The real return vs nominal return trap

The most common mistake in future-value calculations is using a nominal return (say 8% equity historical) without adjusting for inflation. Nominal FV of 10,000 at 8% for 30 years = 100,627. Real FV at 8% nominal minus 2.5% inflation = 5.5% real = 49,840. That's not a rounding error; it's the difference between "I'll be comfortable" and "I'll be fine if I'm careful". For any horizon over 10 years, use real returns or subtract your inflation assumption before entering the rate. The future-value number means nothing if the purchasing power it represents isn't stated.

What rate is honest to use

Equity real returns average roughly 5.5–6% over long periods. Global equity similar. Bonds have historically averaged 1–2% real, although the last decade has been lower. Mixed portfolios typically 4–5% real, depending on the equity/bond split. Cash at current rates (4.5% nominal, close to inflation) is roughly 0% real. The right rate for your projection depends on what you'll actually invest. Using 10% (the flattered nominal equity number) is a setup for disappointment. Using 3% real on a balanced portfolio is a setup for being pleasantly surprised. Neither extreme is useful.

How compounding multiplies small differences

A 1-percentage-point difference in annual return doesn't sound like much, but over 30 years it's roughly 30% more final wealth. At 4% vs 5% on 10,000 over 30 years: 32,434 vs 43,219 — that's a 33% larger pot. That's why small things that persistently move your effective return — fees, tax drag, asset allocation — matter so much over long horizons. They each shave a fraction of a percent; collectively they can account for half of the final wealth you'd otherwise have had.

The opposite direction: present value

The same formula inverted gives you present value — what's a future sum worth today? If someone offers you 50,000 in 10 years instead of money now, what's the equivalent today at a 5% discount rate? 50,000 ÷ 1.05¹⁰ = 30,696. This is the core idea behind DCF valuation, pension commutation factors, and deciding whether to take a lump sum or annuity at retirement. If you're running the future-value direction regularly, understanding the present-value reverse usually sharpens your thinking about time-value trade-offs.

Using future value for goal-setting

A common use is working backwards from a goal. You want 400,000 in 20 years at 6% real. Required monthly contribution: 864. You want it in 25 years instead: 576/month. Five extra years of compounding cuts the monthly amount by a third. That sensitivity is why time horizon is usually the cheapest lever — starting earlier saves meaningful money. The calculator lets you test this by changing the years input while holding other variables constant.

Monthly vs annual contribution

Technically, paying contributions monthly vs annually affects the calculation slightly — a month of early contribution gets one month of extra compounding. Practically, the difference is small: roughly 2–3% over 30 years. What matters much more is whether you contribute consistently rather than exactly when within the year. Automated monthly contributions beat intentionally-scheduled annual ones in practice because the automation survives motivation gaps that the manual version doesn't.

What this calculator can't capture

Real returns are volatile, not smooth. Taxes on gains (outside tax-advantaged wrappers) reduce effective return. Fees compound against you. Personal circumstances change — job loss, divorce, health events can interrupt contribution patterns. Sequence-of-returns risk matters most near withdrawal. Use the future-value figure as a clean central estimate; plan against scenarios that are 20% worse to absorb reality.