Future Value Calculator · Practical guide
How Long Does It Take to Double Your Money?
Divide 72 by your return rate for a quick estimate — at 7%, money doubles in about 10 years with monthly compounding.
At a glance
The Short Answer
Use the Rule of 72: divide 72 by your annual return rate to get the approximate doubling time. At 6%, money doubles in about 12 years; at 9%, about 8 years. With monthly compounding, the exact figures are slightly faster — 11.6 years at 6%.
Interactive tool
Future Value Calculator
Enter your own values, then compare the result with the examples below.
Future Value Projection
Exact Doubling Times by Return Rate
Compounded monthly, the time for any lump sum to double:
| Annual Return | Rule of 72 Estimate | Exact (Monthly Compounding) |
|---|---|---|
| 4% | 18.0 years | 17.4 years |
| 6% | 12.0 years | 11.6 years |
| 7% | 10.3 years | 9.9 years |
| 8% | 9.0 years | 8.7 years |
| 10% | 7.2 years | 7.0 years |
Verify It With the Calculator
You can confirm any doubling time directly: enter $10,000 as the present value, set monthly contributions to zero, pick your rate, and adjust the years until the future value crosses $20,000. At 7%, 10 years returns about $20,097 — just past double, matching the table.
Doubling Compounds: Two Doublings Is 4x
Each doubling period multiplies your money by two again. At 7%, $10,000 becomes roughly $20,000 in 10 years, $40,000 in 20 years, and $80,000 in 30 years — which is exactly what the calculator shows: $81,165 after 30 years. Time in the market, not timing, drives the result.
The Rule of 72 Works in Reverse Too
Divide 72 by an inflation rate to see how fast money loses half its purchasing power. At 3% inflation, prices double — and cash sitting still loses half its value — in about 24 years. It is a quick way to see why a near-zero yield is a slow loss.
Frequently Asked Questions
Why 72 and not 70 or 100?
72 approximates the exact logarithmic math closely for rates between about 4% and 12%, and it divides evenly by most common rates, which makes mental math easy. For very high rates, 69 or 70 is technically more accurate.
Does the doubling time depend on the amount invested?
No. Doubling time depends only on the return rate and compounding frequency — $100 and $1,000,000 double in the same number of years at the same rate.
Do monthly contributions change the doubling time?
They change how fast your balance grows, but the Rule of 72 applies to a fixed lump sum with no additions. With contributions, your balance can double much sooner because new money is arriving.
Does the rule account for taxes and fees?
No. Use your after-tax, after-fee return for a realistic estimate. A 7% return taxed down to 5.5% stretches the doubling time from about 10 to about 13 years.