How long will it take to triple your money? Use the Rule of 115 for a quick estimate and get the exact tripling time at any interest rate.
At 5%, the Rule of 115 says your money triples every 23.0 years (115 ÷ 5 = 23).
Exact calculation: ln(3) / ln(1.05) ≈ 22.5 years.
The rule is off by just 0.5 years at this rate — an error of about 2%.
At 7%, the Rule of 115 estimates 16.4 years to triple your money (115 ÷ 7 ≈ 16.4).
Exact calculation: ln(3) / ln(1.07) ≈ 16.2 years.
The rule is accurate to within 0.2 years at 7% — a very close approximation.
At 10%, the Rule of 115 gives exactly 11.5 years (115 ÷ 10 = 11.5).
Exact calculation: ln(3) / ln(1.10) ≈ 11.5 years.
At 10% the rule and the exact formula agree almost perfectly — 11.5 years either way.
At 12%, the Rule of 115 says 9.6 years (115 ÷ 12 ≈ 9.6).
Exact calculation: ln(3) / ln(1.12) ≈ 9.7 years.
Still very close — the rule is within 0.1 years of the exact value at 12%.
To triple your money in 10 years, you need approximately 11.5% (115 ÷ 10 = 11.5).
Exact rate needed: (3^(1/10) - 1) × 100 ≈ 11.61%.
A $10,000 investment at 11.61% grows to exactly $30,000 in 10 years.
See how accurate the Rule of 115 approximation is for every rate from 1% to 15%. The rule is most accurate for rates between 5% and 15%, which covers most real-world investment returns.
| Rate (%) | Rule of 115 (Years) | Exact (Years) | Difference |
|---|
r = Annual interest rate (as a percentage, e.g., 10 for 10%)
Years to Triple = Estimated time for your investment to grow 3×
ln = Natural logarithm (ln 3 ≈ 1.0986)
r = Annual interest rate (as a percentage)
r = Required annual interest rate (%)
years = Time period in which you want to triple your money
The Rule of 115 comes straight from the mathematics of compound growth. If your money grows at rate r per year, it multiplies by a factor of (1 + r/100) each year. After t years, it has grown by (1 + r/100)^t. To triple your money you need (1 + r/100)^t = 3, which solves to t = ln(3) / ln(1 + r/100).
Because ln(3) ≈ 1.0986, the "perfect" mental-math constant would be 100 × ln(3) ≈ 109.9. The Rule of 115 uses 115 instead because the approximation ln(1 + r) ≈ r slightly under-estimates true growth — using a slightly larger constant compensates for that error, making 115 noticeably more accurate than 110 across the typical range of investment returns (5% to 15%).
Tripling-time mental math is easy: take the interest rate and divide it into 115. At 11.5% → 10 years. At 10% → 11.5 years. At 7% → about 16.4 years. At 5% → 23 years. Because 115 has few convenient divisors, you can round the rate first — at 7.2% use "about 7" and estimate 16–17 years. The rule is designed for quick ballpark answers, not precise forecasts.
The Rule of 115 is an approximation that works best for annual interest rates between 5% and 15%. For rates outside this range the error grows, and for negative rates the rule breaks down entirely (your money never triples if it is losing value). It also assumes interest is compounded annually with no fees, taxes, inflation, or withdrawals — in the real world, those factors can significantly extend tripling time. For precise planning, always use the exact formula ln(3) / ln(1 + r/100).
The Rule of 115 is the tripling cousin of the famous Rule of 72. Where the Rule of 72 estimates how long it takes to double your money, the Rule of 115 estimates how long it takes to triple it: just divide 115 by your annual rate of return (as a percentage), and the answer is the approximate number of years until your money grows 3×.
Why 115? The math behind tripling is identical to doubling, except the target factor is 3 instead of 2. The exact number of years to triple at rate r is t = ln(3) / ln(1 + r/100). Since ln(3) ≈ 1.0986, the theoretically "perfect" shortcut constant would be about 110. The Rule of 115 nudges that number up slightly to compensate for the approximation error in ln(1 + r) ≈ r, which makes 115 remarkably accurate across the realistic range of 5% to 15% annual returns.
The mental math is simple enough for a restaurant napkin: at 11.5% your money triples in about 10 years; at 10% it takes about 11.5 years; at 5% about 23 years. You can even invert the rule — to triple your money in N years, you need roughly 115 ÷ N percent per year. Want to triple in 10 years? Target about 11.5% annually.
Remember that the rule assumes steady, compounded growth. Real investments bounce around from year to year, so treat the result as a planning estimate, not a guarantee.
Both rules are shortcuts for the same compound-growth math — they just target different milestones. The Rule of 72 answers "how long to double?" while the Rule of 115 answers "how long to triple?" Since tripling takes longer than doubling at the same rate, the Rule of 115 always returns a bigger number of years.
| Rate (%) | Double — Rule of 72 | Triple — Rule of 115 | Exact Triple Time |
|---|---|---|---|
| 5% | 14.4 years | 23.0 years | 22.5 years |
| 7% | 10.3 years | 16.4 years | 16.2 years |
| 10% | 7.2 years | 11.5 years | 11.5 years |
| 12% | 6.0 years | 9.6 years | 9.7 years |
| 15% | 4.8 years | 7.7 years | 7.9 years |
Use the Rule of 72 when you are thinking in doubling terms — most savings goals, "double my money" scenarios, and quick inflation checks (72 ÷ inflation rate = years for purchasing power to halve). Use the Rule of 115 when the goal is a 3× milestone: "I want my $10,000 to become $30,000" is a tripling question. For quadrupling, the related Rule of 144 (144 ÷ rate) does the same job. If you need precision for a real financial plan, skip the shortcuts and use the exact logarithmic formulas in this calculator.
The Rule of 115 is a wonderful lens for thinking about long-term investing. At a 10% average annual return — roughly the historic long-run average of the U.S. stock market — your money triples every 11.5 years. Start with $10,000 at age 30, and by age 41 you have $30,000; by about age 53 (two triplings later) you have $90,000; a third tripling brings $270,000 around age 64. Compounding rewards patience enormously.
At a more conservative 7% return — closer to a balanced portfolio — tripling takes about 16 years. That is still powerful: $20,000 triples to $60,000 in 16 years, and to $180,000 in 32. Lower-risk portfolios trade speed for stability; the rule makes that trade-off visible in a single division.
Tripling times are brutally sensitive to costs. A 1% annual fee on a portfolio earning 7% gross drops the net return to 6%, and the tripling time stretches from about 16.2 years to nearly 19 years (exact: ln(3) / ln(1.06) ≈ 18.9). At 5% net after fees and taxes, tripling takes over 22 years. Taxes on realized gains and inflation also quietly extend the real time it takes your purchasing power to triple — which is why low-cost index funds and tax-advantaged accounts matter so much.
1. At typical market returns, plan on tripling roughly every 11–16 years — that is the Rule of 115 at work. 2. Every percentage point of fees or taxes costs you years: at 7% gross, a 1% drag adds about 3 years to tripling. 3. Use the rule to sanity-check ambitious promises — if someone promises to triple your money in 3 years, they are implicitly promising a ~44% annual return, which is far beyond realistic sustained market performance.
Disclaimer: Rules of thumb like the Rule of 115 assume steady compound growth with no fees, taxes, or withdrawals. Investment returns are not guaranteed, and past performance does not predict future results. Market volatility, inflation, taxes, and fees can significantly slow real-world tripling times. This calculator is for educational and illustrative purposes only and is not investment advice. Always consult a qualified financial professional before making investment decisions.