Planning & time calculators
Baby due date calculator
Estimate a due date from your last period, conception date, IVF transfer, or an ultrasound, with current pregnancy week and trimester.
Runs in your browser with no account and no stored data
How it works
Pick the calculation mode that matches what you know best: first day of last period, conception date, IVF transfer date, or ultrasound pregnancy age. The calculator returns an estimated due date plus the current pregnancy week and trimester from the dates you enter.
From last period: due date = first day of last period + 280 days, adjusted by (cycle length − 28) days. From conception: due date = conception date + 266 days. IVF: Day 3 transfer + 263 days, Day 5 transfer + 261 days. From ultrasound: gestational start = scan date − gestational age in days, due date = gestational start + 280 days. Pregnancy week = floor((today − gestational start) / 7) + 1.
Last period 1 January with a 28-day cycle → due date about 8 October. Conception around 15 January. If today is 1 March, you are in week 9 of pregnancy (first trimester).
Planning a pregnancy timeline, understanding how different dating methods point to slightly different dates, mapping trimesters and milestones, or checking IVF and ultrasound-based estimates. It is a timing tool, not a medical decision tool.
What do you want to do next?
Want to plan further? Estimate the conception date or browse baby names for inspiration.
FAQ
Is this medical advice?+
No. This calculator gives a date estimate based on standard pregnancy dating rules. Talk to a healthcare professional for an accurate due date and any medical guidance.
How is the due date estimated?+
From your last period, the calculator adds 280 days (40 weeks). From a conception date it adds 266 days. IVF dates use 263 days for a Day 3 transfer and 261 days for a Day 5 transfer. From an ultrasound it works backwards from the gestational age you enter.
What if my cycle is not 28 days?+
Enter your cycle length and the calculator adjusts the due date by the difference from 28 days. A longer cycle usually means later ovulation and a slightly later due date.
How are the pregnancy week and trimester worked out?+
Pregnancy is dated from the first day of the last period (the gestational start). The calculator counts the days from that date to today, then shows the current week, days into the week, and the trimester (1: weeks 1–13, 2: 14–27, 3: 28+).
Why does my ultrasound date sometimes differ from my last period date?+
Ovulation timing varies, so an early ultrasound is often used to update the dating. The calculator reflects whichever input you choose, and both can be valid.
Which input should I trust most if I have more than one date?+
Use the input you consider most reliable for your situation. The calculator does not decide which method is medically preferred; it only applies the dating rules for the mode you choose.