How Long Does It Take to Double Your Money?

How long does it take to double your money? There's a famous shortcut — the Rule of 72 — that gives you the answer in seconds at any return rate.

Last updated: August 3, 2026Reviewed by CalcGrowth Editorial Team

Quick answer

Divide 72 by your annual return rate. At 6% your money doubles in 12 years; at 8% it's 9 years; at 10% it's roughly 7 years. This shortcut works for any rate up to about 20%.

The Rule of 72

Divide 72 by your annual return rate. The result is the number of years it takes your money to double.

1% return → 72 years to double
3% return → 24 years
5% return → ~14 years
6% return → 12 years
8% return → 9 years
10% return → 7.2 years
12% return → 6 years

The rule is approximate but accurate within a fraction of a year for most returns up to 20%.

Why it works

It's a clever approximation of the exact compound interest formula: years = ln(2) / ln(1 + r). The actual constant is 69.3, but 72 is used because it divides cleanly by many common rates (2, 3, 4, 6, 8, 9, 12).

Real-world examples

Savings account at 4%

$10,000 takes 18 years to become $20,000. By comparison, a high-yield account at 5% does it in 14.4 years.

Index fund at 8% historical average

$10,000 doubles in 9 years → $20K. Doubles again in another 9 years → $40K. After 36 years (4 doublings) → $160,000. That's the power of compound growth on a single deposit.

Aggressive portfolio at 10%

Money doubles every 7.2 years. $10K becomes $640K in 42 years, just from doubling 6 times.

The flip side: doubling costs

The Rule of 72 also applies to debts and inflation:

Credit card at 24%: balance doubles in 3 years if unpaid
Inflation at 3%: prices double in 24 years
Inflation at 6%: prices double in 12 years (1970s-style)

Tripling and quadrupling

Two related rules:

Rule of 114: years to triple. At 8%, money triples in 14.25 years.
Rule of 144: years to quadruple. At 8%, money quadruples in 18 years.

How to use it for retirement planning

If you're 25 with $20K saved at 8%, you can expect approximately:

Age 34: $40K (1 doubling)
Age 43: $80K (2 doublings)
Age 52: $160K (3 doublings)
Age 61: $320K (4 doublings)
Age 70: $640K (5 doublings)

And that's without adding a single dollar more. With monthly contributions, the result is far higher.

Doubling time at a glance

Annual return	Rule of 72	Exact (annual compounding)
3%	24.0 years	23.4 years
5%	14.4 years	14.2 years
7%	10.3 years	10.2 years
10%	7.2 years	7.3 years
12%	6.0 years	6.1 years

Rule of 72 estimate vs the exact compounding result.

The rule of 72 is within a few months of the exact answer for anything between 4% and 12%, which covers almost every realistic long-term assumption.

Worked example: $25,000 left alone

Assume $25,000 invested at 7% with no further contributions:

Year 10: about $49,200 — the first double
Year 20: about $96,700 — the second double
Year 30: about $190,300 — the third double

The point most people miss

The third doubling adds more money ($93,600) than the first two combined. Nothing changed except time in the market. See how compound interest works.

Does doubling time change if I keep contributing?

Yes — new money shortens the time to reach a target balance, but the rule of 72 only describes the growth of money already invested. For contribution schedules use the compound interest calculator.

What is the rule of 114?

It estimates tripling time the same way: 114 ÷ rate. At 7%, roughly 16.3 years.

How long to double money in a savings account?

At 4.5% APY, about 16 years — and inflation erodes much of that. Cash is for safety, not doubling; see how inflation affects your savings.

Key takeaways

Divide 72 by your annual return to estimate doubling time in years.
At 7%, money doubles roughly every 10 years and quadruples in 20.
Later doublings add far more absolute money than early ones.
The rule ignores fees, tax and inflation — subtract those from your rate first.

Use the calculator

See how fast your money doubles

Enter your starting balance and rate to see exact doubling timelines.

Open Compound Interest Calculator

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Frequently Asked Questions

How accurate is the Rule of 72?

Within ~1% accuracy for return rates between 6% and 10%. For very high or very low rates, use the exact formula: ln(2)/ln(1+r).

What rate should I use for my investments?

For long-term diversified stocks, 7% real (after inflation) or 9–10% nominal. For high-yield savings, today's actual rate (4–5%).

Does the Rule of 72 include taxes?

No — use after-tax return for taxable accounts. In tax-advantaged accounts (Roth IRA, 401(k)), use the gross return.

What's the Rule of 70?

Same idea, slightly more accurate at lower rates. 70 ÷ rate = doubling years. Use whichever divides cleanly by your rate.

Does it work for monthly contributions?

The Rule of 72 only works for a single deposit growing untouched. For monthly contributions, use a compound interest calculator.

Is the rule of 72 accurate?

Within a few months for returns between 4% and 12%. Below 3% or above 15% it drifts, and the exact formula ln(2)/ln(1+r) is better.

What return should I assume?

Broad equity markets have historically averaged 7–10% before inflation. Using 7% keeps projections conservative — see [best interest rate assumptions to use](/best-interest-rate-assumptions-to-use).