What is the Rule of 72 table used for?

A Rule of 72 table is a quick lookup that tells you how many years it takes for an investment to double at any given annual return rate. Divide 72 by the rate and you get the years to double. At 8% return, money doubles in 9 years. At 12%, in 6 years.

How accurate is the Rule of 72 table?

Within 1–2% of the exact ln(2)/ln(1+r) value for rates between 4% and 15% — the range covering almost all real-world investments. Less accurate at very low rates (under 2%) and very high rates (over 20%), where the table here also shows the exact value for comparison.

Why does the Rule of 72 use 72 and not 69?

The mathematically exact constant for low rates is 69.31 (= 100 × ln(2) ≈ 69.31%). But 72 has many integer divisors (1, 2, 3, 4, 6, 8, 9, 12, 18, 24, 36, 72), making mental math far easier. The trade-off: about 1% accuracy loss at typical investment rates, for a huge gain in usability.

Does the Rule of 72 work for credit card debt?

Yes, with a small underestimate at high APRs. A 24% credit card APR means unpaid debt doubles in roughly 3 years (72 ÷ 24 = 3). Exact answer: 3.22 years. Still a powerful mental tool to understand how fast revolving debt grows.

Reference table · Updated May 2026

Rule of 72 table: 1% to 25%

Look up the years it takes any investment or debt to double, at any whole-percent rate from 1% through 25%. The table shows both the Rule of 72 approximation and the mathematically exact value — so you can see exactly when the shortcut starts to drift.

Quick formula

Years to double = 72 ÷ rate (rate as whole percent, not decimal). 72 ÷ 6 = 12 years. 72 ÷ 8 = 9 years. 72 ÷ 10 = 7.2 years. Inside 1% of the exact answer for any rate between 4% and 15%.

Years to double at every rate, 1%–25%

Annual rate	Rule of 72	Exact	Typical use
1%	72.00 yrs	69.66 yrs	Cash / checking
2%	36.00 yrs	35.00 yrs
3%	24.00 yrs	23.45 yrs	Long-term inflation
4%	18.00 yrs	17.67 yrs
5%	14.40 yrs	14.21 yrs	HYSA / CDs
6%	12.00 yrs	11.90 yrs
7%	10.30 yrs	10.24 yrs	S&P 500 real return
8%	9.00 yrs	9.01 yrs
9%	8.00 yrs	8.04 yrs
10%	7.20 yrs	7.27 yrs	S&P 500 nominal
11%	6.55 yrs	6.64 yrs
12%	6.00 yrs	6.12 yrs
13%	5.54 yrs	5.67 yrs
14%	5.14 yrs	5.29 yrs
15%	4.80 yrs	4.96 yrs	Avg credit card APR (low)
16%	4.50 yrs	4.67 yrs
17%	4.24 yrs	4.41 yrs
18%	4.00 yrs	4.19 yrs	Personal loans
19%	3.79 yrs	3.98 yrs
20%	3.60 yrs	3.80 yrs
21%	3.43 yrs	3.64 yrs
22%	3.27 yrs	3.49 yrs	Avg credit card APR (high)
23%	3.13 yrs	3.35 yrs
24%	3.00 yrs	3.22 yrs	Subprime / store cards
25%	2.88 yrs	3.11 yrs

The exact column uses the closed-form t = ln(2) / ln(1 + r) where r is the decimal rate. For example, at 10% the exact doubling time is ln(2) / ln(1.10) = 7.27 years; the Rule of 72 gives 7.2 — a 1% miss.

How to read this table

Investments: find your expected return, read off years to double. A $10K balance at 8% becomes $20K in 9 years, $40K in 18, $80K in 27.
Inflation: at 3% inflation, purchasing power halves every 24 years. Same math, opposite direction.
Debt: at 22% APR, unpaid card debt doubles in about 3.3 years. Minimum payments barely stay ahead of the doubling.
Goal-based reverse: if you want money to double in 8 years, you need 72 ÷ 8 = 9% return.

Related Rule of X tables

Rule of 114 — years to triple your money. 114 ÷ 8 = 14.25 years.
Rule of 144 — years to quadruple. 144 ÷ 8 = 18 years.
Rule of 70 — slightly more accurate at low rates (under 5%). 70 ÷ 2 = 35 years to double at 2%.

Plug your own numbers in

For exact projections with monthly contributions and inflation adjustments, use our calculators.

Exact values computed as t = ln(2) / ln(1 + r/100). For continuously compounded rates, doubling time is ln(2) / r ≈ 69.31 / R (percent), where R is the rate as a percent.