For a single deposit, future value follows FV = P × (1 + r/n)^(n·t). Adding regular contributions stacks an annuity term: PMT × [((1 + r/n)^(n·t) − 1) / (r/n)]. The tool runs the same recurrence month-by-month so you also get a per-year breakdown of contributions vs interest. All math is local — your inputs never go to a server, useful when modelling private financial scenarios.


              FV = P · (1 + r/n)^(n·t)  +  PMT · ((1 + r/n)^(n·t) − 1) / (r/n)

Common use cases

Projecting how a brokerage account grows with a fixed monthly contribution.
Comparing the effect of monthly vs annual compounding on the same rate.
Estimating the time required to reach a savings goal.

Frequently asked questions

Is this nominal or real?

Nominal. Inflation is not subtracted. To get a real return, lower the rate by your assumed inflation rate.

Does it tax interest?

No — pre-tax. Apply your own rate to interest earned in a taxable account.

Why does monthly compounding give slightly more than annual?

Each month the existing balance earns a small amount that itself earns interest the following month. The effective annual rate is (1 + r/12)^12 − 1, marginally above r.

Can I model variable contributions?

Not currently — fixed monthly amount only. For irregular cash flows you need a spreadsheet.

Embed this tool

Add this free compound interest calculator to your own website or blog — copy the code below and paste it into your page HTML. No signup, no API key.

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📈 Compound Interest Calculator

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