How this calculator works
IVF dating uses the embryo age and transfer date, rather than the date of the last period. At transfer, conventional gestational age is embryo age plus 14 days. The 40-week estimated due date does not change for twins. Reverse mode is calendar planning only: treatment scheduling depends on clinical and laboratory factors and cannot ensure a particular birth date. Day 6 follows the same embryo-age arithmetic as the guideline examples for day 3 and day 5. The result is an estimate for information only and is not medical advice.
Formula
EDD = transfer date + 266 - embryo age (days). Transfer date = target EDD - (266 - embryo age).
Worked example
A day-5 transfer on 2026-01-01 gives EDD 2026-09-19; a day-3 transfer on that date gives 2026-09-21.
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Frequently asked questions
Does fresh versus frozen transfer change the arithmetic?
The relevant values are the actual transfer date and embryo developmental age, not time spent frozen.
Should twins have an earlier due date here?
The dating convention is unchanged. Recommended delivery timing is a separate clinical decision.
Can reverse mode schedule treatment?
No. It gives only the calendar transfer date corresponding to a hypothetical due date.