Financial calculators should show their work. Here’s exactly what ours do, what they assume and how we check that the math is right.
Simple CAGR does one thing: help you understand how money and businesses grow over time. We stay away from mortgages, taxes and loans so that each tool here can be clear and well tested.
Every calculation runs in your web browser. The amounts you type are never sent to us. There’s no sign-up and there are no ads. See the privacy page for what we do measure.
All eight calculators use the same small calculation engine. The charts, tables and even the worked examples in our articles are produced by that same code, so the writing can’t disagree with the math.
Every formula has automated tests, including zero growth, losses, partial years, very large numbers and bad input. If a test fails, the site doesn’t get updated.
Rates are yearly and “effective.” When you enter 8%, we mean the value grows 8% over a year. When we need a monthly rate, we use the one that compounds to exactly 8% over twelve months, (1.08)1/12 − 1, instead of 8 ÷ 12.
Contributions go in at the end of each period unless you choose otherwise on the Investment Growth Calculator. Yearly contribution raises happen once a year.
Dates use 365.25 days per year to account for leap years. Holding periods are counted in calendar days.
Nothing is rounded until it’s displayed. We calculate at full precision and only round when showing you the answer.
Results are illustrations, not forecasts. They assume a steady rate and leave out taxes, fees, inflation and the ups and downs of real markets, unless a page says otherwise. Use them to understand trade-offs and compare scenarios, and talk to a qualified professional before making big decisions.
| Test case | Result |
|---|---|
| CAGR: $10,000 to $25,000 over 5 years | 20.11% |
| CAGR: $10,000 to $8,000 over 5 years | −4.36% |
| Future value: $10,000 at 8% for 20 years | $46,609.57 |
| Reverse CAGR: $100,000 target, 8%, 10 years | $46,319.35 |
| Doubling time at 8% | 9.01 years |
| Investment growth: $10,000 + $250 a month, 8%, 20 years | $188,859.34 |
These are a few of the cases our automated tests check on every update. You can reproduce any of them with a spreadsheet or a financial calculator.