Cost of Delay Calculator

The cost of delay quantifies the compound growth forfeited by postponing the start of regular investing. Because compound interest generates returns on previous returns, early contributions are disproportionately valuable. A single £5,000 contribution at age 25 growing at 7% for 40 years reaches £74,872. The same £5,000 invested at age 35, with 30 years left to grow, reaches only £38,061. That £36,811 gap is almost half the final value, and none of it comes from paying in less. The money is identical, and only the time it spends compounding has changed.

For regular monthly contributions, the cost of delay is even more dramatic. Starting at age 25 with £300 a month at 7% accumulates approximately £787,000 by age 65. Delaying ten years and paying the same £300 a month for 30 years reaches only £366,000, a cost of delay of about £421,000. Catching up is harder than most people expect. To finish level with the early starter, the delayed investor would need to contribute approximately £645 a month, more than double the original amount, since the missing years cannot be bought back at any price.

The calculator compares starting now with starting after your chosen delay, showing both final pots, what each of you paid in, the cost of waiting and how much of that cost is lost growth rather than missed contributions. It then works out the monthly amount the late starter needs to finish level, and a small table repeats the sums for delays of 1, 5 and 10 years. Even brief hesitation registers. Missing a single month of compound growth at 8% costs roughly 0.67% of the lifetime outcome, which is why waiting for a more comfortable moment to begin is usually the expensive option.

The same arithmetic runs through the rest of a household's finances. Paying £100 a month into a pension from age 25 at 6% builds around £199k by 65, while starting at 35 produces about £100k, so a decade of delay costs roughly half the eventual pot. Mortgage overpayments follow the same logic in reverse. Directing £200 a month at the balance early in the term saves £20-£50k of interest compared with making identical overpayments late on, because interest is charged on what is still outstanding rather than on the original loan.

Some delays cost money because a window shuts rather than because growth is missed. The £20,000 ISA allowance cannot be carried forward, so an unused year simply disappears. Selling a UK residential property with Capital Gains Tax to pay starts a 60-day clock from completion to report and pay it, with penalties for missing it. Underpaid PAYE accrues HMRC interest, running above 7% in 2026, which turns an administrative delay into a debt that compounds against you. None of that appears in a projection of investment growth, but it belongs in the same column of the ledger.