How this calculator works
Canadian Blood Services currently states minimum whole-blood intervals of 56 days for donors registered as male and 84 days for those registered as female. This page adds that many calendar days to the previous donation using UTC arithmetic, including leap days. A custom interval supports another blood service or an individually assigned wait. The date is an interval calculation only: iron status, temporary deferrals, programme changes and the donor service assessment can delay donation further. The result is an estimate for information only and is not medical advice.
Formula
Next date = previous donation date + required calendar days. Previous date = next date - required days. Interval = next date - previous date.
Worked example
A previous donation on 1 January 2026 plus 56 days gives 26 February 2026. Adding 84 days gives 26 March 2026. In leap year 2024, 1 January plus 56 days gives 26 February as well.
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Frequently asked questions
Does the date guarantee eligibility?
No. The donor service makes the final eligibility decision at donation.
Can I use this for plasma or platelets?
Only with the correct service-specific custom interval. The built-in policies are for whole blood.
Why use days rather than months?
Donation intervals are expressed in days; months have unequal lengths and can give the wrong date.