Planning · Investing
See how your money grows
Start with any principal, add a monthly contribution, and watch the power of compounding turn small, consistent investments into real wealth.
Projection
Final balance-
Total contributions-
Interest earned-
Growth over time
Formula
Final balance = P × (1 + r/n)n·t + PMT × ((1 + i)m − 1) / i, where P = principal, PMT = monthly contribution, r = annual rate, n = periods/year, t = years, m = total months, i = monthly rate.
Compound interest — frequently asked questions
What is the rule of 72?
It's a shortcut to estimate doubling time: divide 72 by the annual return rate. At 8%, your money doubles about every 9 years. At 6%, every 12 years. It's not exact, but it's a surprisingly accurate mental model.
Does compounding frequency matter?
A little. Going from annual to monthly compounding at 7% turns 10,000 over 20 years into roughly 40,387 instead of 38,697 — about 4% more. Going from monthly to daily adds only a few more dollars. Contributing regularly matters far more than frequency.
How accurate is this projection?
The math is exact for the inputs you provide, but real-world returns vary year to year. Think of the result as an expected value, not a guarantee. Planning with 1–2% below historical averages builds in a healthy safety margin.
Financial guides to go deeper
Short, practical reads that pair with our calculators.
Compound Interest vs. Loan Interest
Why the same force that builds wealth also keeps debt spiraling.
Credit CardsThe True Cost of Paying Only the Minimum
A $5,000 balance at 24% APR becomes decades and more-than-doubled cost at the minimum.
LoansThe Surprising Power of Extra Payments
Real numbers on how $50–$200 extra per month reshapes any long-term loan.