Compound Interest

See how savings grow with compounding and optional monthly contributions.

How Compound Interest works

Project compound growth with yearly, quarterly, monthly or daily compounding plus monthly contributions. Everything happens inside this page: the tool reads your input, runs the calculation or conversion locally, and hands the result back to you. Nothing is transmitted, because there is no backend to transmit it to.

That design choice is deliberate. Most free tool sites upload your files to a server, process them there, and quietly keep a copy. Toolcin cannot do that — the site is a set of static files. If your connection dropped the moment the page finished loading, every tool would still work.

The formula and the compounding frequency

The tool computes A = P(1 + r/n)^(nt), where P is the starting amount, r the annual rate as a decimal, n the compounds per year and t the number of years. Interest is then A − P.

Frequency changes the answer because interest starts earning interest sooner. Ten percent compounded yearly on 100,000 gives 259,374 after ten years; compounded monthly it gives 270,704. The monthly figure is higher because each month's interest joins the balance twelve times a year instead of once.

Compounding	n	Balance after 10 years at 10% on 100,000
Yearly	1	259,374
Quarterly	4	268,506
Monthly	12	270,704
Daily	365	271,790

Monthly contributions

A recurring deposit needs a different formula, because each contribution compounds for a different length of time. The tool handles it by adding the contribution at each period and letting it compound for the remaining periods, which is the standard future-value-of-an-annuity approach.

Order matters: contributions made at the start of each month earn one extra month of interest compared with contributions at the end. The difference over ten years is roughly one month's interest on the final balance — small per month, visible over decades.

What the number does not include

Tax on interest, account fees, inflation and currency movement are all excluded. A nominal 10% return with 8% inflation is about 2% real growth, and a 1% annual fee compounds against you just as relentlessly as the interest compounds for you.

Treat the output as the arithmetic of a stated rate, not a forecast of an investment.

Good to know

Works offline once loaded, including on flights and in locked-down networks.
No file size limit beyond your device's own memory.
Free to use, with no account and no usage counter.
Results are produced locally, so they are not logged or shared with anyone.

Questions

What is compounding?

Interest earning interest — the reason a 10% annual return beats 10% simple interest over time.

Does it include tax or inflation?

No, both are ignored, so real returns will be lower.

What is the difference between compound and simple interest?

Simple interest is paid only on the principal; compound interest is paid on principal plus accumulated interest. Over long periods the gap is enormous — see the simple interest page for the side-by-side.

Does it account for tax?

No. Enter a post-tax rate if you want an after-tax figure.

How this number is produced

The calculation is A = P(1 + r/n)^(nt), plus a future-value-of-annuity step for monthly contributions, following standard compound interest mathematics. The formula is repeated here so the result can be checked by hand rather than taken on trust.

This is a calculator, not advice. No clinician, accountant or adviser has reviewed it, and it cannot see your circumstances. For anything involving health, a loan, a tax filing or a religious obligation, confirm the figure with a qualified professional or the authority that publishes the rule.

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