See how a lump sum and regular monthly contributions grow over time with compound interest. Compounding means you earn returns on your returns - the engine behind long-term saving and investing.
Your savings plan
£
£
%
yrs
Future value
£108,959
After 20 years at 6%
Total you put in£53,000
Compound growth£55,959
Final balance£108,959
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How compounding works
Compound interest means each period's interest is added to your balance, so future interest is calculated on a larger amount. Over long periods the effect snowballs: the gap between simple and compound growth becomes dramatic, and starting earlier matters more than contributing more later.
Worked example
5,000 lump sum + 200/month for 20 years at 6% a year.
Total contributions = 53,000.
Future value about 108,000 - roughly 55,000 of it is compound growth.
Real returns also depend on charges, tax and inflation. Holding investments in an ISA shelters the growth from UK tax - see the ISA calculator - and the inflation calculator shows what your pot will be worth in today's money.
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Frequently asked questions
What return rate should I assume?
Cash savings rates move with the Bank of England base rate. For diversified stock-market investing, many people model a long-run nominal return of around 5-7% before inflation and charges - but returns are never guaranteed.
How often does interest compound here?
This calculator compounds monthly, which matches most savings accounts and regular-investment plans and is a sensible default for long-term projections.
Report a bug or ask a question about this calculator
Important: BrickCrunch provides general information and estimates only — this is not financial, tax, mortgage or legal advice. Calculations are simplified and your circumstances may differ. UK tax and rate figures are checked against gov.uk (21 June 2026 (2026/27 tax year)) but rates change and errors are possible. Always confirm figures with gov.uk or a qualified professional before making decisions.
