Pregnancy Due Date Calculator

From the moment the test shows two lines, the first question is when. This calculator answers it four different ways — from the first day of your last menstrual period, from a known conception date, from an IVF embryo transfer, or from an ultrasound measurement — and then turns the date into a living timeline of the whole pregnancy.

The classic method is Naegele's rule: 280 days (40 weeks) from the first day of the last period, which this tool refines with your actual cycle length, since longer or shorter cycles shift ovulation and with it the due date. IVF dating is the most precise of all because the embryo's age is known exactly — a day-5 blastocyst transfer is dated 261 days from transfer, a day-3 transfer 263 — and the ultrasound option accepts the gestational age a sonographer measured, the dating clinicians ultimately rely on.

Around the date itself you get context that makes the number useful: how many weeks and days along you are today, your trimester, a progress bar and countdown, an estimated conception date, a table of key dates (end of the first trimester, the 18–22-week anatomy-scan window, viability at 24 weeks, full term at 37), a milestone timeline, and the traditional week-by-week size comparison from poppy seed to small pumpkin. One honest note the tool repeats: a due date is an estimate — only about one baby in twenty arrives on it, most healthy births fall within two weeks either side, and the date from your doctor's dating scan takes precedence over any calculator.

Each method converts your input into an estimated due date (EDD) by whole-day arithmetic:

• LMP: EDD = last period + 280 days, adjusted by (your cycle length − 28), since ovulation shifts with cycle length.
• Conception: EDD = conception + 266 days (280 minus the assumed 14 days to ovulation).
• IVF: EDD = transfer date + 261 days for a day-5 blastocyst or + 263 for a day-3 transfer — both equivalent to 266 days from fertilization.
• Ultrasound: EDD = scan date + (280 − gestational age at scan in days).

Everything else derives from the EDD: your gestational age today is counted from the implied cycle start (which is why pregnancy is "40 weeks" though conception happens around week 2), trimesters switch at 14 and 28 weeks, and the key dates are fixed offsets on the same timeline. Baby-size figures are widely used patient-education estimates by completed week — illustrative, not diagnostic.

A due date is a statistical midpoint, not a delivery appointment — only around 4–5% of babies arrive on it, and normal healthy births span 37 to 42 weeks. LMP dating degrades with irregular cycles; conception dating assumes you truly know the date; and the tool's milestone and size figures are general patient-education values, not measurements of your pregnancy. It cannot confirm a pregnancy, assess viability, or detect complications — as its own disclaimer says, your doctor or midwife's assessment, especially the dating scan, always takes precedence.

All date math is whole-day arithmetic on local dates, client-side. Method offsets: LMP +280 days with (cycle − 28) adjustment; conception +266; IVF +261 (day-5) or +263 (day-3); ultrasound +(280 − GA in days). Gestational age today derives from the EDD-implied cycle start and is validated to 0–320 days; trimesters switch at 14 and 28 weeks; progress is GA/280. Baby size, milestones, and key dates are fixed lookups keyed to completed weeks. Nothing is transmitted or persisted.

The four dating methods

Newly pregnant people wanting a date and timeline before the first appointment; IVF parents who want their precise transfer-based dating applied correctly; partners and families following along week by week; and anyone planning leave and logistics around the anatomy scan, third trimester, and full term. It complements — never replaces — the dating your midwife or doctor provides.