See how your money grows over time. Enter your starting amount, monthly contributions, and interest rate.
| Year | Deposits | Interest | Balance |
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Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. It's often called "interest on interest" and is the reason long-term investing is so powerful.
Where: P = principal, r = annual rate, n = compounds per year, t = years, PMT = regular contribution
The difference between simple and compound interest grows dramatically over time. £10,000 at 6% simple interest earns £600/year forever. With monthly compounding, year 1 earns £617 — but by year 20, you're earning £1,964 that year alone on the same initial £10,000.
A quick way to estimate how long it takes to double your money: divide 72 by your interest rate. At 6%, your money doubles roughly every 12 years. At 8%, every 9 years.
Use the tax rate field above to see the impact of tax on your returns. Set to 0% for ISA or pension calculations.
More frequent compounding produces slightly higher returns. For £10,000 at 6% over 10 years:
The difference is small for typical savings rates but becomes meaningful at higher rates or over longer periods.