How long does it take to double money in Excel

Q: How long to triple money?

Use 3 as the future value: =NPER(B2,0,-1,3).

Q: What return do I need to double in 8 years?

Use RATE: =RATE(8,0,-1,2), about 9.05%.

Formula (Excel and Google Sheets)

=NPER(B2,0,-1,2)

Use NPER with a present value of -1 and a future value of 2: =NPER(B2,0,-1,2) gives the years to double.

Result on the example: 10.2 in B3
Works in: Every current version
Google Sheets: Same formula

See it work

The formula is already in B3. Change any input and the result updates, or edit the formula to experiment.

How it works

NPER counts the periods for 1 to grow into 2 at the given rate, with no payments in between. At 7% a year that takes 10.2 years. The amounts don't matter, only the ratio, which is why 1 and 2 are enough.

=NPER(B2,0,-1,2)

Result10.24476835

B27.0%
The value in B2.
-1-1
Makes the value negative.
NPER(B2,0,-1,2)10.24476835
NPER: Number of periods to pay off or reach a target.
- rateB27.0%
- pmt0
- pv-1-1
- fv2

In Google Sheets

The same formula works in Google Sheets: =NPER(B2,0,-1,2). We ran it in Google Sheets mode on the same data and it returns 10.2.

Other ways to do it

Each one was run on the same example sheet.

Formula	Result	When to use it
=LN(2)/LN(1+B2)	10.2	The exact math behind it: the logarithm of 2 divided by the logarithm of the growth factor.
=72/(B2*100)	10.3Different result	The rule of 72, a mental shortcut: 72 divided by the percentage. Rule of 72: 10.3 years.

Common mistakes

Use the rate per period. For a monthly rate, the result is in months.
The rule of 72 drifts at high rates; at 20% it says 3.6 years against an exact 3.8.

Try it yourself

Same data, empty answer cell. Your formula is graded instantly, then re-checked on changed data, so a typed-in number won't pass.