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 the Army One-Site Tape Test Works and How to Estimate Your Score

By the Super Simple Digital Tools Team · Updated June 2026

The Army Body Composition Program exists to keep soldiers within a healthy body composition range, and in 2024 it moved to a simpler way of measuring it. Where the old method required taping multiple sites and applying log-based equations, the current one-site test asks for just your body weight and the circumference of your abdomen. That change makes the assessment faster, more consistent between graders, and easy to replicate at home, which is exactly what this calculator does.

The process starts with a screening, not a tape. Each soldier is first checked against a height and weight table for their age and sex. If you fall at or under the maximum screening weight for your height, you meet the standard and no tape test is needed. Only when you exceed that weight does the abdominal measurement come into play to determine your body fat percentage, so knowing your number in advance tells you whether the tape will ever come out.

Taking the measurement correctly matters more than people expect. Use a flexible tape that does not stretch, remove belts and bulky clothing, and stand tall with feet about hip-width apart. Place the tape at the level of your navel, keep it horizontal all the way around, and snug it against the skin without compressing the tissue. Read it at the end of a relaxed breath out. Because a single reading can be off, the Army takes three and averages them to the nearest half inch.

Once you have weight and abdomen in hand, the formula does the rest. Men and women use different equations because body fat distributes differently, but both depend only on those two inputs. Plug your averaged abdomen measurement and current weight into the calculator and it returns an estimated percentage. The tool then compares that figure to the maximum allowed for your age group, giving you a clear pass or work-needed signal rather than just a raw number.

Treat the output as a planning tool. Trends matter more than any one reading: track your estimate every couple of weeks as you train, and you will see how abdominal measurement responds to changes in diet and conditioning. When an official assessment is on the calendar, measure under the same conditions each time so your home estimates stay comparable, and remember that your unit's graded result is the one that counts on the record.

  • Average three abdomen readings to the nearest half inch, just as a grader would, instead of trusting a single measurement.
  • Measure at the navel at the end of a relaxed exhale, and never suck in or push your stomach out.
  • Compare your weight to the height and weight screening table first; if you are under it, the tape test may not apply at all.
  • Re-check your estimate at the same time of day and in similar conditions so progress between sessions is genuinely comparable.

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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