Compound Interest Calculator
Future value from principal, rate, compounding frequency, years, and optional monthly additions. Click any i for detail.
Growth
Starting principal ($)
i
Principal
Amount already invested. |
|
|---|---|
Annual rate (%)
i
Rate
Nominal annual rate before compounding. |
|
Compounds per year
i
Compounds
12 = monthly, 4 = quarterly, 1 = annual, 365 = daily sketch. |
|
Years
i
Years
Time invested. |
|
Monthly addition ($)
i
Monthly addition
Optional contribution each month (converted to the compounding frequency). |
How to use this calculator
- Enter starting principal and annual rate.
- Pick compounding frequency and years.
- Add monthly contributions if you save along the way.
Results explained
Lump sum uses P(1+r/n)^(nt). Monthly additions are modeled as an ordinary annuity at the same compounding frequency.
Quick reference: compounding
Same 7% looks different by frequency.
| Item | Detail |
|---|---|
| Annual 7% | ×1.0700 / yr |
| Monthly 7% nominal | Effective ≈ 7.23% |
| Rule of 72 | 72 ÷ rate ≈ years to double |
| CD APY page | Use when the bank quotes APY |
Taxes, fees, and sequence-of-returns risk are not modeled.
How the estimate is built
FV_lump = P(1+r/n)^(nt). Annuity FV uses PMT × ((1+i)^n − 1)/i.
Example scenario
$10,000 at 7% monthly for 20 years plus $200/mo ≈ a much larger nest egg than the lump alone — read the live total.
FAQ
APY vs nominal rate?
If your bank quotes APY, use the CD APY calculator. This page uses nominal rate + frequency.
Start-of-month vs end?
Ordinary annuity (end of period) sketch.
Inflation?
Pair with the inflation calculator for real purchasing power.