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Rule of 72

The classic mental-math shortcut: how many years an investment needs to double at a given return.

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2Stosujemy wzór
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Jak używać

  • Enter Annual return %.

Wzór

Years to double ≈ 72 ÷ annual return %.

Przykład

At 8% a year, money doubles roughly every 9 years (72 ÷ 8).

About this calculator

The rule of 72 is the fastest way to feel compound growth without a calculator: divide 72 by the return and you have the doubling time. It turns abstract percentages into a timeline — the language in which long-term decisions actually get made.

Its real power is comparison. 6% doubles money in 12 years; 8% in 9; the two extra points of return are 'one extra doubling' over a working lifetime — the honest argument for keeping fees low and starting early.

Częste pytania

How accurate is it?

Very good between about 4% and 15%; it drifts at extremes. It's a shortcut, not a substitute for the compound formula.

Is there a rule for tripling?

Yes — divide 115 by the return: at 8%, tripling takes about 14.4 years. We show it in the breakdown.

Does it work for inflation too?

Yes, in reverse: at 6% inflation, prices double (money halves) in about 12 years.

Wskazówki

  • Time in the market beats timing the market.
  • Reinvest returns to let compounding work.
  • Keep fees low — they compound against you.

Pojęcia

Compounding
Earning returns on past returns.
CAGR
The smoothed annual growth rate.
Yield
Income as a percent of price.