Investment Calculator

How it works

Each month: balance = balance × (1 + i) − fee + contribution, with i = (1 + r/n)^(n/12) − 1 · No fees or raises: FV = P × (1 + i)^N + C × ((1 + i)^N − 1) ÷ i · Real value = balance ÷ (1 + inflation)^years

The initial amount P and every monthly contribution C compound at the monthly rate i that matches your annual return r and compounding choice n, for N months. Because growth builds on prior growth, the final years add the most. Under More options you can make contributions at the start of each month, raise them by a set percent each year, and subtract a yearly fee such as a fund’s expense ratio, charged as 1/12 of the rate on the balance every month. Change Calculate to work backwards from a target: the monthly contribution and the starting amount are solved exactly (the balance is a straight-line function of each), while the return needed and the time needed are found by trial. The inflation line divides each balance by cumulative inflation so you can read it in today’s buying power.

Worked example

$10,000 plus $300 a month at a 7% return compounded monthly for 20 years: the monthly rate is 0.07 ÷ 12 = 0.5833%. The initial amount grows to $40,387 and the contributions to $156,278, for $196,665 — $82,000 of it contributions and $114,665 growth. At 2.5% inflation that is about $120,019 in today’s dollars. A 0.5% yearly fee would cut the balance to about $183,618: $7,866 of fees plus the growth they would have earned, $13,047 in all. To reach $250,000 in 20 years you would need about $402 a month; at $300 a month it takes 22 years 10 months.

Sources: Investor.gov (SEC) — Mutual fund fees and expenses

Frequently asked questions