£10,000 Compounded: 20 years vs 30 years
Same starting amount, same rate — different horizon. Here's what extra time does to the final balance.
After 20 years vs 30 years at 5%
- 20 years: £26,532.98
- 30 years: £43,219.42
- Extra growth from the extra 10 years: £16,686.45
The headline insight: the extra 10 years isn't worth 10/20 more — it's worth 63% more. That's the non-linear compounding tail.
Full calculator pages
Why the tail is so big
Compound interest is front-loaded in absolute terms but back-loaded in growth. In the first 20 years, £10,000 grows to £26,532.98 — a gain of £16,532.98. In the additional 10 years that follow, it almost doubles again to £43,219.42, because each year's gain is percentage-of-a-larger-number. This is the reason that starting a pension at 25 rather than 35 is almost always worth more than working an extra year at the end of your career.
At different rates
- 3% (cash ISA long-term): £18,061.11 after 20y, £24,272.62 after 30y
- 5% (balanced portfolio): £26,532.98 after 20y, £43,219.42 after 30y
- 7% (equity tracker long-term average): £38,696.84 after 20y, £76,122.55 after 30y
Real vs nominal return
These figures are nominal — they ignore inflation. At 3% long-run CPI, the £43,219.42 after 30 years has purchasing power equivalent to roughly £17,805.83 in today's money. Compounding still wins, but the real-return figure is what matters for long-term planning.