Age on a date
Find completed age on any selected date. You do not have to use today as the reference date.
Understand the numbers · Make life easier
Due date and pregnancy weeks
Estimate a due date and pregnancy weeks from a known reference. Choose the first day of the last menstrual period or a clinician-confirmed due date.
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Gestational age on the selected date
20 weeks 0 days
This estimates dates only. For irregular periods or uncertain dates, use a due date confirmed by a clinician.
Additional days0 days
Estimated due date2026-10-08
Time until due date140 days
Worked steps
- For a regular 28-day cycle: first day of the last period + 280 days.
- 140 days = 20 weeks and 0 days.
- Date estimates cannot confirm pregnancy or replace prenatal care.
Last-period mode assumes a regular 28-day cycle and adds 280 days to the first day. For irregular cycles, IVF or uncertain dates, use a clinician-confirmed due date. Only calculates dates from 0 weeks to 42 weeks 6 days. Does not confirm pregnancy, assess fetal development or replace ultrasound and prenatal care.
Method and scope
Last-period mode assumes a regular 28-day cycle and adds 280 days to its first day. Confirmed-due-date mode counts pregnancy days relative to that due date and the same 280-day reference.
The reference field changes meaning with the selected mode. A due date is an estimate and is not a guaranteed delivery date.
For irregular cycles, IVF or uncertain dates, use the due date confirmed by a clinician. The tool only displays 0 weeks through 42 weeks 6 days; it does not confirm pregnancy, assess fetal development or replace ultrasound and prenatal care.
References:Johns Hopkins: due dates and the 28-day-cycle assumption、NHS: due dates and ultrasound confirmation
What this helps you do
Estimate a due date and pregnancy weeks from a known reference. Choose the first day of the last menstrual period or a clinician-confirmed due date.
What to enter
Start with known date type, then fill the other relevant fields in the units shown. The field hints explain the required format and examples.
How the calculation works
Last-period mode assumes a regular 28-day cycle and adds 280 days to its first day. Confirmed-due-date mode counts pregnancy days relative to that due date and the same 280-day reference.
Worked example
A last-period first day of 2026-01-01 gives an estimated due date of 2026-10-08. On 2026-01-29 the date-based pregnancy age is four weeks.
Understanding the answer
The reference field changes meaning with the selected mode. A due date is an estimate and is not a guaranteed delivery date.
Scope and limitations
For irregular cycles, IVF or uncertain dates, use the due date confirmed by a clinician. The tool only displays 0 weeks through 42 weeks 6 days; it does not confirm pregnancy, assess fetal development or replace ultrasound and prenatal care.