Compound Interest Calculator
See how your money can grow over time. Enter your details to visualize the power of compounding.
Future Value after 20 years
$561,314
Total Contributions
$250,000
Total Interest Earned
$311,314
Time to double your money
9.9 years
Rule of 72 estimate: ~10.3 years
How this works
Balances compound at your chosen frequency (default monthly) using the nominal annual return you enter (default 7%) — this calculator does not deflate for inflation, so figures are in future, not today's, dollars.
Each period the balance grows first, then the monthly contribution is added, simulated month by month for accuracy regardless of the display frequency chosen.
Key assumptions
- Default annual return 7%, compounded monthly by default (annually, semiannually, and quarterly are also selectable).
- Contributions are constant in nominal dollars for the full time horizon — no contribution growth.
What this leaves out
- Inflation — unlike every other calculator in this suite, this one reports nominal future-dollar figures, not today's-dollars figures.
- Fees — expense ratios and advisory fees are not deducted from the return.
Related calculators
A worked example: $10,000 and $1,000 a month for 20 years
Start with $10,000, add $1,000 every month, compound monthly at 7% a year, and run it for 20 years. The ending balance is $561,314. Of that, $250,000 is money you put in — the initial $10,000 plus $240,000 of contributions — and $311,314 is growth.
The shape of the curve matters more than the endpoint. At the 10-year mark the balance is $193,181, against $130,000 contributed, so growth is $63,181 — about a third of the balance. Over the second decade, contributions add another $120,000 while growth adds $248,133. Same contributions, four times the growth, because the second decade compounds on a balance the first decade had to build.
One important convention: unlike the FI-focused calculators on this site, this one reports nominal future dollars and does not deflate for inflation. $561,314 in 20 years is not $561,314 of today's purchasing power — at 2.5% inflation it is closer to $342,000. Use this calculator for growth mechanics, and the FI calculators when you need figures in today's dollars.
Frequently asked questions
Is this figure in today's dollars or future dollars?
Future, nominal dollars. This is the one calculator on the site that does not adjust for inflation, because the question it answers — how does a balance grow at a given rate — is a nominal one. Every other projection here runs on the real return and reports in today's purchasing power. If you want the comparable real figure, either enter a return already net of inflation, or divide the result by (1 + inflation) raised to the number of years.
Does the compounding frequency setting change the answer much?
Less than most people expect. Moving from annual to monthly compounding at the same nominal rate adds a fraction of a percent to the effective annual rate, and the gap barely widens beyond monthly. The inputs that actually move the result are the contribution, the time horizon, and the rate itself. The setting is there for accuracy against a specific product's terms, not as a lever.
When are contributions added — before or after growth?
After. Each month the balance grows first, then the contribution lands, which is the end-of-period (ordinary annuity) convention used consistently across this site. Contributing at the start of each month instead would add roughly one extra month of growth to every contribution — a small effect per month, a visible one over 20 years. If your real contributions land early in the month, treat the result as marginally conservative.
Is 7% a reasonable return to assume?
It is the site default because it approximates long-run US equity returns of roughly 10% nominal less about 3% inflation, rounded down. But note the inconsistency if you use it here: 7% is a real-return figure being applied in a nominal calculator. If you want a genuinely nominal projection, 9-10% is the historical analogue, and the resulting number will be in dollars worth substantially less than today's. Either way, treat any single rate as a rough magnitude — no real portfolio returns the same percentage every year.
Why does the model not deduct fees?
Fees are not modeled anywhere on this site, and over long horizons they are not a rounding error. A 1% annual expense ratio against a 7% return costs roughly a seventh of your growth, compounded. The simplest workaround is to subtract your all-in fee from the return you enter — 6% instead of 7% for a 1% fee — which approximates the drag closely enough for planning.
Sources
- Compound Interest Calculator
U.S. Securities and Exchange Commission (Investor.gov) — checked 2026-08-12
The SEC's own investor-education compound interest calculator, covering the same mechanic (initial amount, recurring contribution, horizon, rate) this calculator models.
*The calculations provided are for illustrative purposes only and should not be considered financial advice. Please consult with a qualified financial professional before making any decisions.