Savings & Compound Interest Calculator

Compound interest means each period's interest is calculated on the balance so far — including interest already earned in previous periods — rather than only on the original deposit. This calculator projects that growth from an initial lump sum, a regular contribution, an annual interest rate, and a term in years: each period, interest is applied to the existing balance first, then that period's contribution is added, so a new contribution itself only starts earning interest the following period.

Worked example: £1,000 saved up front plus £100 added every month at 4% annual interest grows to roughly £15,500 after 10 years — of which about £2,500 is interest earned, on top of the £1,000 initial deposit and £12,000 in contributions. Small differences in the rate or the regularity of contributions compound into large differences over a long enough term, which is what the chart on this page is for.

The full breakdown below the chart shows total contributed versus total interest earned at every point along the timeline, not just the final balance — useful for seeing how much of a long-term projection is actually your own money going in, versus interest the balance has earned on top of it.