Rule of 72

Client

Quick mental math for compound growth doubling time—divide 72 by the annual percent rate.

How to use

Enter annual interest rate as a percent (e.g. 8).

About Rule of 72

Estimate years to double an investment from an annual rate using the rule of 72—browser-only. The interactive transform on this page runs in your browser tab—Toolcore does not need your paste for the core operation described above.

How to use this page

Paste or type in the main workspace, run the primary action from the toolbar, then copy or download the result. Use Load example when the page offers it, or URL prefill (?q= / ?qb=) so agents and tickets open the same input.

At 8% per year, doubling time ≈ 9.00 years (rule of 72).

Nearby workflows on Toolcore

  • Simple interest calculator — I = P·r·t for principal, annual rate %, years—no compounding. when units or numeric output should be checked on a related calculator.
  • Compound interest calculator — Principal, APR, and compounding—future value, interest earned, and APY for savings-style growth. when units or numeric output should be checked on a related calculator.
  • ROI percentage — Return on investment from final value and initial cost. when units or numeric output should be checked on a related calculator.
  • Percent change — Calculate percentage increase or decrease from an old value to a new one—local math in your browser. when units or numeric output should be checked on a related calculator.

Common use cases

  • Estimate when savings might double at a given APY.
  • Sanity-check compound growth assumptions.

Common mistakes to avoid

  • Negative rates

    The rule applies to positive growth rates.

FAQ

Exact formula?

This is an approximation; compound interest tools give precise values.

More tools

Related utilities you can open in another tab—mostly client-side.