Exact dates, day-count conventions, a year-by-year breakdown, simple-vs-compound comparison, doubling time, and tax-adjusted returns. All instant, all in your browser.
Pick which value you want the calculator to work out — the other three fields become your inputs.
Simple interest grows in a straight line — the same interest amount is added every year.
See how much more (or less) you'd earn if the same rate compounded instead.
Exact time (not an approximation) for a lump sum to double or triple at a given simple interest rate.
Estimate what you actually keep after tax on the interest earned above.
See what your maturity amount is really worth once inflation is factored in.
Saved only on this device — never uploaded anywhere. Click an entry to reload it.
Simple Interest = Principal × Rate × Time / 100, where Rate is the annual percentage rate and Time is in years. The maturity amount is Principal plus Interest.
Simple interest is calculated only on the original principal for the whole term. Compound interest is calculated on the principal plus any interest already added, so it grows faster over time.
A day-count convention defines how the number of days between two dates becomes a fraction of a year, such as Actual/365, Actual/360, or 30/360. Different conventions produce slightly different interest for the same dates.
Switch the "Solve for" tab to Principal, Rate, or Time. The calculator rearranges the simple interest formula and fills in the field you're solving for using the other three values.
Doubling time is how long it takes an investment to double, calculated as 100 divided by the annual rate. Unlike compound interest's Rule of 72, this is an exact formula.
Yes. Enter your marginal tax rate in the Tax-Adjusted Returns panel to see your after-tax interest and effective after-tax rate.
No. Every calculation runs locally in your browser. Local history is stored only in this browser's local storage and is never uploaded.
Yes. Toggle Date Mode, pick a start and end date, and the calculator works out the exact day count and converts it to years using your chosen day-count convention.
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