Compound Interest Calculator

How to use 3 steps

Enter the Starting amount and pick the Currency.
Set the Annual rate, Years, Compounds and anything Added each period.
Press Calculate to see the final balance and the interest earned.

Starting amount

Currency

Annual rate (%)

Years

Compounds

Added each period

Projected balance

These figures are estimates. They use standard formulas and are useful for planning and comparison, but they are not financial advice. A lender or provider will apply their own fees, compounding conventions, rounding and local rules, so their figures will differ from these. Check the actual offer before committing to anything. Contributions are treated as paid at the end of each compounding period. Inflation, tax and charges are not modelled, so the real spending power of the final figure will be lower.

How this tool works

Projects how a balance grows from a starting amount, a rate and a number of years, with optional regular contributions, and shows the balance year by year.

Compounding means interest is calculated on interest already earned, so growth accelerates rather than accumulating in a straight line. The frequency matters as well as the rate: the same nominal rate compounded monthly produces slightly more than compounded annually, because each period's interest starts earning sooner. Regular contributions are treated as arriving through the period rather than all at the start, which is the conservative reading. Everything here is a projection from constant assumptions — no real investment returns the same percentage every year.

What a projection is not

A constant rate is an assumption, not a forecast: real returns vary, and a sequence of poor early years leaves a different result from the same average arriving in a different order.
Inflation is not deducted: the final figure is in nominal terms. At three per cent inflation, money loses roughly half its purchasing power in twenty-four years.
Tax and charges are excluded: platform fees, fund charges and tax on gains all reduce the real outcome, and small annual percentages compound against you exactly as returns compound for you.
Time does more work than rate: an extra decade usually outweighs an extra percentage point, which is why the year-by-year table is worth reading rather than just the total.

Why growth accelerates rather than accumulates in a straight line

Compounding means interest is calculated on interest already earned, not only on the original balance, so each period's growth becomes part of the base the next period grows from. The [msm_tool slug="compound-interest-calculator"] projects that curve from a starting amount, a rate, a number of years and any regular contributions, showing the balance year by year rather than only the final total.

How often interest compounds changes the outcome too

The same nominal rate produces a slightly larger result compounded monthly than compounded annually, because each month's interest starts earning its own interest sooner rather than waiting for the year to close. Regular contributions are treated as arriving through the period rather than all at its very start, which is the more conservative of the two reasonable readings.

A constant rate is an assumption, not a forecast

No real investment returns the same percentage every single year, and a sequence of weak early years produces a different final balance from the identical average return arriving in a different order across the same span. Everything the projection shows follows directly from holding the rate perfectly constant, which is a simplification rather than a prediction of what will actually happen.

The result is nominal, not adjusted for inflation

The final figure represents future money at face value, with nothing deducted for the fact that a given sum buys less over time. At three per cent inflation, money loses roughly half its purchasing power over twenty-four years, which is worth holding in mind against any total this projection produces for a genuinely long horizon.

Fees and tax reduce the real outcome and are not included

Platform fees, fund charges and tax on gains all work against the balance exactly the way returns work for it — compounding, quietly, over the same span of years. A charge of even one per cent annually becomes a substantial sum once compounded across decades, despite looking negligible in any single year.

Time usually outweighs rate

An extra decade in the projection typically moves the final balance more than an extra percentage point of return does, which is the reason the year-by-year table is worth reading in full rather than jumping straight to the total at the end — it shows where the growth is actually concentrated across the span, not just how much accumulates by the finish.

Frequently Asked Questions

Specific to the Compound Interest Calculator. Broader questions about this category are answered on the category page.

What is compound interest?

Interest calculated on the accumulated balance, including interest already earned, rather than on the original amount alone. Each period's growth becomes part of the base for the next, which is what makes the curve bend upwards over long periods.

How does compounding frequency change the result?

More frequent compounding gives a slightly higher effective return for the same nominal rate, because interest starts earning sooner. The gap between annual and monthly compounding is real but modest — far smaller than the effect of the rate or the time period.

Does this account for inflation?

No. The projection is in nominal terms. To think in today's money, subtract your inflation expectation from the rate before entering it — that gives a real rather than nominal projection.

Is this a prediction of what I will have?

No. It shows what constant assumptions produce. Actual returns vary year to year, and the order in which good and bad years arrive changes the outcome even when the average is identical. Treat it as a way of comparing scenarios.

Are fees and tax included?

No. Platform fees, fund charges and tax on gains all reduce the outcome and compound against you over time. A charge of one per cent a year is a large sum over decades.