Compound interest means investors earn returns on both their original principal and the interest that principal has already produced. The Consumer Financial Protection Bureau (CFPB) states that compound interest is earned "on the money you've saved and on the interest you earn along the way"CITE:E1. The Federal Reserve Bank of St. Louis describes the same mechanism from a saver's perspective: compounding means "earning interest on your original principal—plus on the interest your investment generates"CITE:E2. In both framings, each period's interest becomes part of the base for the next period's interest, which is the foundation for estimating how fast an investment grows.
The Rule of 72 is a shortcut for estimating how many years an investment needs to double, using only its expected annual rate of return. The Federal Reserve Bank of St. Louis calls it "an easy compound interest calculation to quickly determine how long it will take to double your money based on the interest rate"CITE:E6. The U.S. Securities and Exchange Commission (SEC) explains that "if you know your investment's expected rate of return, the Rule of 72 can tell you approximately how long it will take for your investment to double in value"CITE:E3. The calculation itself is a single division: the SEC instructs investors to "simply divide the number 72 by your investment's expected rate of return (ignoring the percent sign)"CITE:E4.
A 9% annual return doubles an investment in about eight years, while a 12% return shortens that to about six years. The SEC illustrates the formula with a 9% return: "your investment will double in value about every 8 years (72 divided by 9 equals 8)"CITE:E5. The Federal Reserve Bank of St. Louis provides a second data point at a higher rate: "at a 12% interest rate, it would only take six years to double your money"CITE:E7.
| Expected Annual Rate of Return | Rule-of-72 Calculation | Years to Double |
|---|---|---|
| 9% | 72 ÷ 9 | 8 |
| 12% | 72 ÷ 12 | 6 |
What this means: The SEC's and the Federal Reserve Bank of St. Louis's figures, read together, show that raising the expected annual return from 9% to 12% — a three-percentage-point difference — cuts the doubling period from eight years to sixCITE:E5CITE:E7. That gap is a direct expression of the compounding mechanism described by the CFPB and the St. Louis Fed: because interest already earned keeps generating further interest, a higher expected return compounds that effect faster, shortening the number of years the Rule of 72 assigns to doublingCITE:E1CITE:E2.
Divide 72 by the investment's expected annual rate of return, ignoring the percent sign, as described by the SEC<CITE:E4>.
The Rule of 72's real value is as a quick gut-check rather than a precise forecast: dividing 72 by an expected return turns an abstract percentage into a concrete number of years, which is exactly how the SEC frames the tool. The comparison laid out here is instructive on its own terms — moving from a 9% to a 12% expected return cuts the doubling period from eight years to six, a difference produced entirely by how much interest compounds on interest each period. The one input worth watching when applying this rule to any investment is simply the expected annual rate of return being plugged into the formula, since that single number is what the entire eight-year or six-year estimate hinges on.
Google announced a €13 billion ($15.1 billion) investment in Finnish AI infrastructure to be deployed in 2027–2028, its largest single investment in Europe. The plan covers new data centers in Kajaani, Muhos, and Vaala plus an expansion in Hamina, backed by a 22-year power deal for 50% of Loviisa nuclear plant output and projected to support 37,000 construction-phase jobs and 7,000 permanent roles.
Chenbro (勤誠, 8210) reported August 2026 revenue of NT$2.457 billion, roughly flat month-on-month (-0.2%) but up 40.5% from a year earlier. Cumulative January–August revenue reached NT$19.848 billion, up 51.7% year-on-year.
Chang Hwa Bank (TWSE: 2801) reported cumulative after-tax profit of NT$15.567 billion for January through August, up 23.21% year-on-year with EPS of NT$1.29, a record for the period. The bank attributed the gain to loan, deposit, and wealth management momentum, and August alone delivered NT$2.916 billion in profit, up 29.16% year-on-year.