Doubles in
5 yrs
Rule of 72: 4.8 yrs
Doubling your money at 15%
How long does it take to double your money at 15%? Estimate it with the Rule of 72 and compare it with the exact value — with a growth curve and a live calculator. Illustrative only, not investment advice.
At 15%, money doubles in about 4.8 years (Rule of 72), or 4.96 years exactly.
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Explore doubling time
Pick a starting amount and a target — the rate stays fixed at 15%. The estimate and the exact value update live.
Fixed rate: 15% per year. $10,000 grows to 2× its value.
Estimate (rule)4.8 yrs
Exact4.96 yrs
Resulting amount$20,001
Growth of $10,000 at 15%
8× after about 15 years
Double, triple, quadruple at 15%
Rule estimate (72, 114, 144 ÷ 15) versus the exact logarithmic value and the difference.
| Target | Rule | Estimate | Exact | Difference |
|---|---|---|---|---|
| Double | 72 | 4.8 yrs | 4.96 yrs | -0.16 |
| Triple | 114 | 7.6 yrs | 7.86 yrs | -0.26 |
| Quadruple | 144 | 9.6 yrs | 9.92 yrs | -0.32 |
Doubling time by rate (1–20%)
15% · 4.8 years
Accuracy: Rule of 72 vs. exact
Rule of 72Exact
15% · rule 4.8 vs. exact 4.96 yrs
Common amounts doubled at 15%
What $1,000 to $100,000 becomes when doubled at 15% — and after how many years.
| Starting amount | Doubled | Doubles in |
|---|---|---|
| $1,000 | $2,000 | 5 yrs |
| $5,000 | $10,000 | 5 yrs |
| $10,000 | $20,000 | 5 yrs |
| $25,000 | $50,000 | 5 yrs |
| $100,000 | $200,000 | 5 yrs |
Milestones at 15%
Triples in
7.9 yrs
Exact, ln(3) ÷ ln(1 + r)
Quadruples in
9.9 yrs
Exact, two doublings
Tenfold in
16.5 yrs
Exact, ln(10) ÷ ln(1 + r)
Why 72 — and where the estimate drifts
The exact doubling time comes from ln(2) ÷ ln(1 + r). For small rates that is roughly 100 · ln(2) ≈ 69.3 — but 72 divides far more easily in your head (by 1, 2, 3, 4, 6, 8, 9, and 12). At 15%, the rule estimates 4.8 years versus 4.96 exactly. The rule is most accurate near 8%; at very low or very high rates the gap grows.
Every figure on this page is illustrative only and not investment advice — real returns vary and are never guaranteed. For your own rate, use the Rule of 72 calculator. Background: Investopedia — Rule of 72.
Related rates & tools
Frequently asked questions
How long does it take to double money at 15%?
The Rule of 72 estimates it fast: 72 ÷ 15 ≈ 4.8 years. The exact formula ln(2) ÷ ln(1 + 15%) gives 4.96 years. For most rates the estimate and the exact value sit only a fraction of a year apart.
When does money triple or quadruple at 15%?
Use Rule of 114 for tripling (114 ÷ 15) and Rule of 144 for quadrupling (144 ÷ 15). Exactly, money triples at 15% after about 7.9 years and quadruples after about 9.9 years.
Why the number 72 specifically?
The exact doubling time is ln(2) ÷ ln(1 + r). For small rates this is roughly 100 · ln(2) ≈ 69.3 — but 72 divides cleanly in your head (by 1, 2, 3, 4, 6, 8, 9, 12). That convenience is why 72 became the standard shortcut.
How accurate is the Rule of 72 at 15%?
At 15%, the rule estimates 4.8 years versus 4.96 exactly. It is most accurate near 8% and drifts a little at very low or very high rates — but as a mental shortcut it stays useful across the whole range.
How long until money grows tenfold at 15%?
Tenfold takes about 16.5 years at 15% exactly (ln(10) ÷ ln(1 + 15%)). A handy shortcut is the "Rule of 231": 231 ÷ 15 gives a similar estimate.
Are these figures investment advice?
No. This page explains the math of doubling time at 15% and is not investment, tax, or legal advice. Real returns vary and are never guaranteed.
Run your own rate
The Rule of 72 calculator opens pre-filled with 15% and shows doubling, tripling, and exact times for any rate.