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Due date calculator

Estimate a pregnancy due date, current week and trimester milestones.

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Due date calculator
Paste a date and this tool works out an estimated due date, the current week of pregnancy, and the trimester it falls in. It supports the three ways a due date is usually counted: from the first day of the last menstrual period (LMP), from a known conception date, or from an IVF embryo transfer date — each one is read differently, and the tool converts all three to the same "day zero" before doing the math.
The calculation method controls how the anchor date is interpreted. LMP uses Naegele's rule — 280 days from the last period — and can be adjusted for a cycle longer or shorter than the textbook 28 days with the cycle-length option. Conception adds the standard 266-day gestation from the moment of conception. Embryo transfer accounts for the embryo's age at transfer (day 3 or day 5). Turn on trimesters and milestones to see the start of the second and third trimesters and the full-term (37-week) mark alongside the due date, and switch the output between a one-line summary and a timeline. A custom reference date checks the numbers for a specific day instead of today.
Paste one date per line to check several pregnancies at once — twins from two donor cycles, or a quick comparison of how the estimate shifts between methods. Dates can be typed as YYYY-MM-DD, DD.MM.YYYY or DD/MM/YYYY (ISO is always accepted no matter which format is selected), and the output uses whichever format you chose. A line that isn't a valid date, or one that would place the pregnancy after the reference date, is reported next to that line rather than blocking the rest.
Everything runs locally in your browser — the dates you enter are never uploaded or stored anywhere. This estimate follows standard obstetric formulas and does not replace a clinical dating scan; use it as a planning reference. When you're done, copy the result, download it as a .txt file, or send it to the input of another tool to keep working with the dates.
FAQ
How accurate is Naegele's rule?
It assumes a 28-day cycle with ovulation on day 14, so it is an estimate, not a diagnosis — most births happen within a couple of weeks of the calculated date. A dating ultrasound is more accurate for an individual pregnancy.
Why does the due date change when I switch the calculation method?
Each method starts counting from a different reference point. LMP counts from the last period, conception counts 266 days from fertilization, and IVF transfer accounts for the embryo already being 3 or 5 days old at transfer — they should agree closely for the same pregnancy once the offsets are applied correctly.
What does the cycle-length adjustment do?
It shifts the standard 280-day estimate by the difference between your average cycle length and 28 days, which moves the estimated ovulation date accordingly. It only applies to the last-menstrual-period method.
Can I enter more than one date?
Yes. Paste one date per line and each is calculated independently using the same options, which is useful for comparing methods or checking multiple pregnancies at once.
Is my data uploaded anywhere?
No. The calculation runs entirely in your browser using standard date arithmetic — nothing you enter is sent to a server or stored outside your device.