How are Premium Bonds odds calculated?

Each £1 bond has the same monthly chance. We use NS&I’s odds per £1 and their published counts by prize tier to compute per-tier probabilities, any-prize odds, and expected winnings.

What inputs do I need?

Enter your bond holding and time period. Optionally add a purchase date—bonds must be held for a full calendar month before entering a draw.

Do more bonds increase my chances?

Yes. Odds scale linearly with how many £1 bonds you hold, up to NS&I’s maximum holding limit.

What does expected winnings mean?

Expected winnings are the statistical average over time given the prize distribution. Actual outcomes vary—our Monte Carlo ranges show typical variability.

How often do you update the data?

Monthly, after NS&I publishes the new prize mix and odds per £1. We display the data month on the page.

OPTIMLY Calculators | Premium Bonds Odds Calculator - Probability & Expected Winnings

Premium bond inputs

Bond holdings

Time period

Prize fund rate (NS&I)

Savings rate for comparison