Retirement Savings Calculator
How it works
What you already have saved compounds on its own — currentSavings · (1+r)ⁿ — while each month's new contribution compounds for a different number of months depending on when it went in. Adding those all up is exactly what an annuity's future-value formula does in one step: contribution · ((1+r)ⁿ − 1) / r. The two pieces add together because they do not interact — money already saved and money added later both grow at the same monthly rate independently of each other — and r and n are the monthly rate and number of months so contributions are compounded on the same schedule they arrive.
Total growth is simply the future value minus everything that was ever put in (current savings plus every monthly contribution) — the portion of the final number that came from returns rather than from your own deposits.
Frequently asked questions
What annual return should I use?
There is no correct answer — it is an assumption you are making about the future, not a fact this calculator knows. Long-run US stock market averages are often cited around 7-10% before inflation, but any given decade can land well outside that range. Try a few different rates rather than trusting one number, and lean conservative if this is money you are counting on.
Why compound monthly instead of yearly?
Because contributions arrive monthly. Compounding yearly would need to pretend each year's contributions all landed on day one (overstating growth) or day 365 (understating it) — compounding every month, in step with when the money actually goes in, avoids picking either wrong answer.
What does this not account for?
Inflation and fees, most importantly. The future value shown is in today's dollars only if the return you entered is already inflation-adjusted, and it does not subtract any fund or account fees, which quietly reduce real-world returns over decades. Treat the result as a clean, before-cost projection, not a guarantee of spending power at retirement.