How it's calculated
The calculator steps month by month (up to 100 years). Each month the balance grows by g = (1 + R)1/12, where R is the annual return treated as an effective annual rate, and then your contribution is added. It stops at the first month the balance reaches the goal.
Each month: B = B·g + c (c = monthly contribution, raised once a year if you choose)
Goal check: B ≥ Goal·(1 + inflation)^(months/12)
Exact formula (constant contribution, no inflation), with i = g − 1:
months = ln[(Goal·i + c) / (Current·i + c)] / ln(1 + i)
months = (Goal − Current) / c if i = 0
The calculator reports this number rounded up to a whole month.
- The return is the same every year. Real returns vary, so the actual date could be years earlier or later.
- No taxes or fees. Contributions are made at the end of each month.
- With inflation set, "$1 million" means $1 million of today's buying power, which is a moving target.
Worked examples
1. $25,000 saved, $1,000 a month, 7%
It takes 26 years and 1 month (313 months) to reach $1,000,000, at about age 56 if you're 30 today. You contribute $338,000.00 (including the starting $25,000); the rest of the $1,002,047.18 balance, $664,047.18, is growth. Load this example
2. Starting from zero with $500 a month at 8%
Here i = 1.081/12 − 1 = 0.6434% a month. months = ln[(1,000,000 × 0.006434 + 500) ÷ 500] ÷ ln(1 + 0.006434) = 410.01, rounded up to 411 months: 34 years and 3 months. Load this example
3. A million in today's dollars
Same as example 1, but the goal rises 3% a year with inflation. It now takes 43 years and 4 months, and the nominal goal by then is $3,599,811.31. Load this example
Frequently asked questions
How long will it take to become a millionaire?
It depends on three things: what you start with, how much you add each month, and your return. For example, from $0, investing $500 a month at an assumed 8% takes about 34 years; $1,000 a month with $25,000 already saved at 7% takes about 26 years. Enter your own numbers above.
How much do I need to invest per month to be a millionaire?
Use the savings goal calculator to answer it that way around: enter $1,000,000 as the goal and the number of years, and it shows the monthly amount needed.
Should I account for inflation?
If you want $1 million of today's buying power, yes. A million dollars 30 years from now buys much less than it does today. Set an inflation rate and the goal grows with it.
What return should I use?
Nobody can promise one. Savings accounts pay a stated rate; stock market returns vary widely from year to year and over decades. Trying a cautious, a middle and an optimistic rate shows how sensitive the answer is.