What rate should I use?

For long-term US stock returns, 7% real (after inflation) or 10% nominal is the historical average. Bonds: 3-5%. Savings accounts: 0.5-5%. Crypto: don't use a fixed rate.

Does compounding frequency really matter?

A little. At 7%/year, monthly compounding gives ~7.23% effective vs 7.00% annual. Real-world impact is small compared to picking a better rate.

Compound Interest Calculator

Future value of an investment growing with compound interest.

Result

Future value

$170,619.05

Future value

$171k

Contributed$70,000(41%)

Earned$100,619(59%)

Initial principal$10,000.00
Total contributions240 monthly deposits$70,000.00
Interest earned$100,619.05
Effective multiplierfinal value ÷ contributions2.44×

How to use this calculator

Enter your starting balance (or 0 if you're starting fresh).
Add a realistic monthly contribution you can actually maintain.
Use 7% as a long-term US stock-market average; 4% for bonds; 10%+ is optimistic.
Compare 20 vs 30 years to see the late-stage compounding effect.

About this tool

Compound interest is the engine behind nearly every long-term wealth-building strategy. This calculator shows what your money becomes when it earns returns, and those returns earn returns. Enter an initial deposit, optional monthly contributions, the expected annual return, and how long you'll let it grow. Try changing the time horizon — the difference between 20 years and 30 years isn't 50% more, it's often 3× more, because the late years compound on a much larger base. Compounding frequency (monthly vs. annual) matters less than people think; what really moves the needle is rate of return and time.

Frequently asked

Each year your interest earns interest. After 30 years at 7%, $1 grows to ~$7.61 — over 7× the original. Most of that growth happens in the final third.