How long to double my money?
The return is only part of the story when you ask how fast money doubles: regular top-ups speed it up, while tax and inflation shrink what the money can buy. Enter a starting sum, expected return, monthly saving, tax drag and inflation, and the calculator tells you when the balance doubles in dollars and when it doubles in real purchasing power. The chart and table show how much steady saving moves that date.
Your balance year by year
The dollar balance and its value in today's money, against a line at twice your starting sum.
How extra saving moves the date
Years to double at your return, tax and inflation, with different monthly additions.
| Added each month | Doubles in dollars | Doubles in real terms | Balance after 10 years |
|---|
How the doubling date is found
The calculator moves through the months one at a time, growing the balance and adding your saving, until it reaches twice the starting sum. It repeats the run in today's money to find the real doubling date.
Return after tax
Tax on each year's gains cuts the rate that gets to compound.
net return = return × (1 − tax)
Monthly growth
The yearly rate is converted into a monthly rate.
monthly = (1 + net return)1/12 − 1
Every month
Grow the balance, then add the month's saving.
balance = balance × (1 + monthly) + added
In today's money
The same run with growth reduced by inflation and additions in today's dollars.
real return = (1 + net return) ÷ (1 + inflation) − 1
Doubling date
The first month the balance reaches double the starting sum.
balance ≥ 2 × start
Doubling your money: FAQ
How many years does it take to double money?
With a steady return and no additions, about 72 divided by the yearly return in percent; at 7 percent, a little over 10 years. Regular monthly additions get you there much sooner, while tax and inflation push the real doubling date later.
Do my monthly additions count towards doubling?
Here they do: the dollar balance doubles when it hits twice the starting sum, whether the extra came from growth or saving. A growth-only figure is shown too, so you can see how much the returns did on their own.
What is doubling in real terms?
It means your money buys twice what it buys today. Prices rise every year, so a balance that doubles in dollars might only buy 60 or 70 percent more. Real doubling uses your return after inflation.
How much does tax slow things down?
When gains are taxed every year, as savings interest usually is, only part of each year's growth stays to compound. Tax-advantaged accounts, or investments you never sell, compound faster; set tax drag to zero for those.
Which return should I enter?
A cautious long-term figure after fees. Savings accounts and bonds might give a few percent a year; broad stock funds have historically given more, with big swings from year to year. Try a low and a high figure to see the spread.
Is this just the rule of 72?
The rule of 72 is a shortcut for growth only, without tax or inflation. This calculator works month by month, so it can include saving, tax and inflation. Our rule of 72 calculator compares the shortcut with the exact sum.