How this instrument works
This instrument does one specific job: count the days and weeks remaining between today and a due date you already have. It doesn't estimate a due date from a last-menstrual-period date or an ultrasound measurement — those calculations belong to a care provider working from clinical measurements. What this page does is take the day you were given and answer the very practical question of how far away it still is.
The countdown is a straight day-count on the civil calendar, the same subtraction used across this site's other date-span instruments, converted into weeks by dividing by 7. A full-term pregnancy is conventionally described as about 40 weeks, or 280 days, measured from the first day of the last menstrual period to delivery — the standard US clinical dating convention; a due date near the middle of a pregnancy will show a totalWeeks figure meaningfully under 40, since this page is counting down to delivery, not counting up gestational age from conception.
Because today's date pre-fills automatically, checking back on a different day naturally shows a smaller countdown than the day before — there's nothing to re-enter beyond the due date itself. Bookmark the page with your due date in the second field and the days-remaining figure updates itself on every visit.
- Leave the first field on today's date, or set it to any date you want the countdown measured from.
- Enter your due date in the second field.
- Read days until your due date, and the same span converted to weeks, directly beneath the inputs.
- Check back on a later day and the countdown updates automatically since today's date refills itself.
Worked example — due date 20 January 2027
With today's date at 2026-07-28 and a due date of 2027-01-20, the instrument reports 176 days remaining, which comes to 25 complete weeks.
That 25-week figure describes the countdown to delivery, not gestational age — a pregnancy dated from the last menstrual period at this point would typically already be well past its own 25-week mark heading toward 40. The two numbers answer different questions: gestational age counts up from conception dating, this countdown counts down to the date on the calendar.
Questions
Does this calculate my due date for me?
No — it counts down to a due date you already have from a care provider. Estimating a due date from a last-menstrual-period date or an ultrasound involves clinical dating conventions and measurements this page doesn't attempt; enter the day you were given, and this instrument handles only the countdown from today to that day.
Why does the weeks figure not match my gestational age in weeks?
Because they're counting different things. Gestational age counts up from the start of pregnancy, conventionally dated from the last menstrual period, toward a full-term 40 weeks. This countdown counts down from today toward the due date itself — the two numbers move in opposite directions and only both happen to reach zero around the same event, delivery.
Where does the 40-week / 280-day full-term figure come from?
It's the standard convention in US clinical guidance: a full-term pregnancy is described as about 40 weeks, or 280 days, measured from the first day of the last menstrual period to delivery, per NIH's National Institute of Child Health and Human Development. This instrument doesn't calculate that figure itself — it's mentioned here only as context for what a due date typically represents.
What if my due date changes after an updated ultrasound?
Just enter the new due date in the second field — the countdown recalculates from today to whatever date is currently entered, with nothing else to update. Due dates are commonly revised earlier in pregnancy after a dating ultrasound, and this instrument has no memory of a previous entry to reconcile against.
Can I use this to count down to something other than a due date?
Yes — the underlying math is a generic days-and-weeks countdown between today and any future date; a due date is simply the label on the second field. For a countdown built around a different kind of event, this site's time-until, wedding-countdown and vacation-countdown instruments run the identical calculation with different labeling.