Calculate days remaining until an estimated due date, with trimester context. The calculator runs entirely in your browser and pairs a focused answer with the method, assumptions and the related tools worth checking next.
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Review the inputs and select Calculate.
Enter the estimated due date and the date to count from. Alongside the days remaining, the tool works back 280 days from the due date to the implied first day of the last period, and from that reports the gestational age in weeks and days on the counting date and the trimester it falls in.
Nothing is measured directly: gestational age is the count of days from the implied last-period date (due date minus 280 days) to the counting date. Under 14 weeks counts as the first trimester, under 28 weeks as the second, and 28 weeks or more as the third.
For a due date of Monday 15 March 2027 counted from Tuesday 20 October 2026, there are 146 days to go. The implied last-period date is 8 June 2026, which makes the gestational age on the counting date 19 weeks and 1 day — the second trimester.
Every figure derives from the single due date entered and the fixed 280-day assumption. If a scan or a clinician revises the due date, the count and the gestational age change with it, so re-enter the updated date; this is a planning countdown, not a medical record.
Enter the estimated due date and the date to count from. Each step below is a short action rather than a wall of explanation.
Use the most reliable source value available for this input.
Use the most reliable source value available for this input.
Read the result, then copy, print or share a link that reopens the same inputs.
Build the next occurrence of the target date and count the elapsed calendar days from the reference date.
Similar tools answer different questions. Match the inputs and the reference point to the answer you actually need.
The numbers come from your inputs; this shows the shape of the calculation.
Enter the estimated due date — every figure in the result is derived from this one date and the standard 280-day model.
Enter the date to count from — the tool works back 280 days from the due date to the implied first day of the last period.
The days to go, with gestational age and trimester: a due date of Monday 15 March 2027 counted from 20 October 2026 leaves 146 days to go, at a gestational age of 19 weeks and 1 day — the second trimester.
Use exact source inputs, keep the reference date visible and verify any official rule separately.
Set the reference date to the event that actually controls the decision, not to today.
Compare the stated method here against the other tool's convention before assuming an error.
For a neighbouring calculation, open the Gestational Age Calculator or the Pregnancy Due Date Calculator. To understand the reasoning first, read Corrected Age for Premature Babies: A Parent-Friendly Guide.
Choose another focused tool when the underlying question changes.
Understand the calendar rules, edge cases and next steps behind this calculator.
Answers about method, inputs, privacy, boundaries and responsible interpretation.
Alongside the days to go, the tool reports the gestational age in weeks and days on the counting date and the trimester it falls in, both worked back from the due date you enter.
It works back 280 days from the due date to the implied first day of the last period, then counts forward from that date to the counting date. Nothing is measured directly; every figure derives from the single due date and the fixed 280-day assumption.
For a due date of Monday 15 March 2027 counted from Tuesday 20 October 2026, there are 146 days to go. The implied last-period date is 8 June 2026, which makes the gestational age on the counting date 19 weeks and 1 day, in the second trimester.
From the gestational age: under 14 weeks counts as the first trimester, under 28 weeks as the second, and 28 weeks or more as the third.
Re-enter the updated due date. The days remaining, the gestational age and the trimester all change with it, because they are all derived from that one date. This is a planning countdown, not a medical record.
Navjeet Kamboj is the author and editor of Age Calculator Lab. He focuses on making age, date, milestone and planning calculations easier to understand through clearly explained methods, practical examples and responsible limitations.