An instrument for compounding · est. formula 1683
Enter a principal, a monthly habit, and a rate of return. This ledger runs the arithmetic month by month — no shortcuts — and shows you exactly where every dollar of growth came from.
| Year | Contributed to date | Interest to date | Balance |
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This free investment calculator projects how a lump sum and a recurring monthly contribution grow over time under compound interest. Unlike calculators that rely on a single closed-form formula, this one runs a month-by-month simulation, so it correctly handles annual step-ups in your contribution, five different compounding frequencies, and an inflation-adjusted "real value" figure — the kind of detail that matters when you're comparing a retirement plan, a college savings fund, or a brokerage account projection.
Adjust the initial investment, monthly contribution, annual rate of return, compounding frequency, and time horizon on the left, and the ledger on the right updates instantly with a year-by-year balance table, a growth chart, and a breakdown of how much of the final balance came from your own contributions versus earned interest. Save any scenario to compare it later under Ledger History.
Compound interest is interest calculated on both your original principal and on interest already earned in previous periods, so a balance grows faster over time than it would with simple interest.
The more often interest compounds — daily versus monthly versus annually — the sooner earned interest itself starts earning interest, which produces a slightly higher final balance for the same nominal annual rate.
Future value is the raw dollar balance a scenario projects. Real value divides that figure by the effect of assumed inflation, showing what the balance is worth in today's purchasing power.
No. This tool produces educational estimates based on the numbers you enter. Actual investment returns vary and are never guaranteed, so results should not be treated as financial advice.