Doubling time calculator
At a growth rate g per year, doubling takes ln(2) / ln(1+g) years — approximated by the classic rule of 70 for small rates. Enter a rate, or let the tool measure a real series: it finds the years in which a country's published value actually doubled.
By growth rate
From a published series
How to use it
- Rate mode: type an annual growth rate (say 7) and compare the rule-of-70 shortcut with the exact answer.
- Data mode: pick a country and indicator; the tool walks the published series and lists every doubling that actually happened.
FAQ
When is the rule of 70 accurate?
For small rates. At 2% the shortcut says 35.0 years against an exact 35.0; at 10% it says 7.0 versus an exact 7.27 — use the exact formula above a few percent.
What counts as a doubling in data mode?
Every crossing from below n× to at-or-above n× the series' own first published value, for n = 2, 4, 8, 16 — so you see the full ladder, not just the first double.
Does a negative rate mean halving?
A constant negative rate has a halving time of ln(2) / |ln(1+g)|; the tool reports that instead of pretending doubling applies.