Compound Interest Calculator

See how your money grows with compound interest and regular deposits.

%
years
Formula: A = P (1 + r/n)^(n·t)
  • A = future value
  • P = principal (initial investment)
  • r = annual interest rate (decimal)
  • n = compounds per year
  • t = number of years

How to use the Compound Interest Calculator

  1. Enter your starting amount. Your initial investment or savings balance.
  2. Set rate, years & frequency. Your annual rate, time horizon and how often interest compounds.
  3. Add monthly deposits. Optionally include a recurring contribution to see the snowball effect.

Why use our Compound Interest Calculator

Project growth. See your future balance, total interest and total deposited at a glance.
Regular deposits. Add a monthly contribution to model real saving habits.
Any frequency. Compound yearly, quarterly, monthly or daily.

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  • Future value projection
  • Yearly breakdown
  • Monthly deposits
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About the Compound Interest Calculator

The Compound Interest Calculator projects how a lump sum, a stream of regular deposits, or both will grow over time once interest starts earning interest on itself. You enter a starting balance, an annual rate, how often interest compounds, the time horizon, and any recurring contributions, and the tool returns the future value alongside how much of that figure came from your own money versus earned interest. It is built for savers and investors who want a realistic picture of where a savings account, certificate of deposit, or steady investing habit could end up rather than a vague gut feeling about long-term growth.

Reach for this calculator whenever you are weighing a long-horizon decision: comparing two savings accounts with different APYs, deciding whether to add an extra fifty dollars a month to a retirement contribution, or checking how many years it takes a balance to roughly double. Because compounding rewards time more than almost anything else, the calculator is most useful early, when small changes to rate, contribution size, or start date produce surprisingly large differences decades out. It is equally handy for a reality check on optimistic projections, since it shows exactly how much of a headline number is genuine interest.

Under the hood the tool applies the standard formula A = P(1 + r/n)^(nt), where P is the principal, r is the annual rate as a decimal, n is the number of compounding periods per year, and t is the number of years. Each compounding period it adds the period's interest to the balance, then computes the next period on that larger figure. Regular deposits are layered in at their own schedule, so every contribution begins its own compounding run. Choosing daily versus monthly versus annual compounding changes n, and shorter periods earn slightly more, though the gap narrows at lower rates and on smaller balances.

Treat the results as a clean mathematical projection, not a forecast. The calculator assumes your rate stays fixed for the whole term and that contributions never miss, while real savings rates move, markets fluctuate, and inflation erodes purchasing power, so an actual outcome will differ. Taxes on interest are also not deducted. On privacy, every figure is computed in your browser using plain arithmetic; no balance, rate, or contribution amount is uploaded, stored, or shared, so you can model sensitive personal finances without leaving any data behind.

Frequently asked questions

What is the difference between compound and simple interest?

Simple interest is calculated only on your original principal, so it grows in a straight line. Compound interest is calculated on the principal plus all previously earned interest, so the balance accelerates over time, which is why people call it interest on interest.

Does compounding frequency really change how much I earn?

Yes, but usually by a modest amount. More frequent compounding (daily versus annually) earns more because interest is credited and re-invested sooner, though the advantage shrinks at lower rates and on smaller balances. The annual rate matters far more than the frequency.

How do regular contributions affect the result?

Each recurring deposit starts its own compounding journey from the day it is added, so consistent contributions often end up generating more growth than the initial lump sum. The calculator separates total contributions from total interest so you can see each clearly.

What interest rate should I enter?

Use the rate that fits your scenario: for a savings account or CD enter the APY shown by the bank, and for an investment use a conservative expected annual return. The figure is assumed fixed for the whole term, so test a range rather than relying on one number.

Does the calculator account for taxes and inflation?

No. It shows nominal growth before any tax on interest and without adjusting for inflation. To estimate real purchasing power, subtract an expected inflation rate from your return, and remember that interest in a taxable account may be reduced at tax time.

From our blog

How to Use a Credit Card Repayment Calculator to Escape the Minimum-Payment Trap

By the Super Simple Digital Tools Team · Updated June 2026

If you only ever read your credit card statement's minimum payment line, you are seeing the figure designed to keep you in debt the longest. A repayment calculator flips the perspective. Instead of asking what is the least I can pay this month, it answers when will this debt actually be gone and what will it cost me in total. That single reframe is often the difference between drifting in debt for decades and setting a finish line you can plan around.

Start by gathering three numbers from your latest statement: the outstanding balance, the purchase APR, and the minimum payment. Enter the balance and APR, then run the calculator twice. First use the minimum payment to establish your baseline. The payoff time and total interest here are your reality check; for a mid-sized balance at a typical APR, minimum-only repayment can run well over a decade and cost more in interest than the original debt.

Now run it again with a fixed monthly amount you can realistically commit to, even if it is only modestly above the minimum. Because every dollar above the interest charge attacks the principal directly, the effect is non-linear. Industry examples are stark: doubling payments on a large balance can shrink a multi-decade payoff to a couple of years and slash total interest by thousands. Watching the payoff date jump backward as you nudge the payment up is the most motivating part of the exercise.

Use the comparison to make decisions, not just to feel informed. If you carry balances on more than one card, model each separately and direct extra money toward the highest-APR card first while paying minimums on the rest, the avalanche approach that minimizes interest. If a promotional 0% rate is ending soon, calculate the post-promo cost now so the jump does not surprise you. The calculator is at its best as a what-if sandbox for these choices.

Finally, treat the output as a disciplined estimate and pair it with action. The figures assume you add no new charges, so the plan only holds if you stop spending on the card while you pay it down. Re-run the numbers whenever your balance, rate, or budget changes, and consider setting your bank to autopay the fixed amount rather than the minimum so the plan runs itself. The math is simple; the hard part is committing to the payment, and seeing the payoff date makes that commitment easier.

  • Always run the minimum first, then a fixed amount, so you can see in dollars and months exactly what paying extra buys you.
  • Stop using the card while you pay it down, since the payoff estimate assumes no new purchases are added to the balance.
  • With multiple cards, model each one and throw spare cash at the highest APR first to cut total interest fastest.
  • Set up autopay for the fixed amount you chose, not the statement minimum, so your plan sticks without monthly willpower.

Read the full guide →

Tool by the Super Simple Digital Tools Team. Reviewed by our editorial team. Free to use, no signup required.

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