How long to double my money?
How quickly your money doubles depends on more than its return: what you add each month speeds it up, while tax and inflation slow down what it can actually buy. Enter your starting amount, expected return, monthly savings, tax drag and inflation, and this calculator tells you when your balance doubles in dollars and when it doubles in real buying power. The chart and table show how much difference regular saving makes.
Your balance over time
The dollar balance and what it would buy in today's money, against twice your starting amount.
How saving more changes the date
Years to double at your return, tax and inflation, with different monthly contributions.
| Added each month | Doubles in dollars | Doubles in real terms | Balance after 10 years |
|---|
How the doubling date is found
The calculator steps through the months, growing the balance and adding your savings, until it reaches twice your starting amount. It runs the same steps in today's money to find the real doubling date.
Return after tax
Tax on each year's gains reduces the rate that compounds.
net return = return × (1 − tax)
Monthly growth
The yearly rate is turned into a monthly one.
monthly = (1 + net return)1/12 − 1
Each month
Grow the balance, then add your saving.
balance = balance × (1 + monthly) + added
Real terms
The same, but growth is reduced by inflation and contributions are in today's dollars.
real return = (1 + net return) ÷ (1 + inflation) − 1
Doubling date
The first month the balance reaches twice the starting amount.
balance ≥ 2 × start
Doubling questions
How long does it take to double money?
At a steady return with nothing added, it takes about 72 divided by the yearly return in percent. At 7 percent that is just over 10 years. Adding money every month gets you there much sooner, while tax and inflation push the real doubling date further out.
Do monthly contributions count towards doubling?
In this calculator, yes: the dollar balance doubles when it reaches twice what you started with, whether the extra came from growth or savings. The growth-only figure is shown separately, so you can see how much is down to returns.
What does doubling in real terms mean?
It means your money buys twice as much as it does today. Inflation raises prices every year, so a balance that doubles in dollars may only buy 60 or 70 percent more. Real doubling uses your return after inflation.
How does tax slow doubling down?
If gains are taxed every year, as interest in a normal savings account usually is, you only keep part of each year's growth to compound. Investments in tax-advantaged accounts, or held without selling, compound faster. Set the tax drag to zero for those.
What return should I use?
Use a cautious long-run figure after fees. High-yield savings and bonds might return a few percent a year, while a broad stock fund has historically returned more but with big swings from year to year. Try a low and a high figure to see the range.
Is this the same as the rule of 72?
The rule of 72 is a shortcut for the growth-only case with no tax or inflation. This calculator works month by month, so it can include savings, tax and inflation. Our rule of 72 calculator compares the shortcut with the exact maths.