Estimate when your baby is due. This free due date calculator works from your last period, conception date or IVF transfer, shows how far along you are today, and gives the estimated conception date.
Based on a typical 40-week (280-day) pregnancy from the last period. If your cycle isn’t 28 days, the estimate is adjusted accordingly.
Estimates only and not medical advice. A dating ultrasound and your healthcare provider give the most accurate due date, especially with irregular cycles.
How the Due Date Calculator Works
This tool estimates a baby’s due date from whichever starting point you know best — the first day of your last period, a known conception date, or an IVF embryo transfer date — and also shows how far along you are today. It’s built on the standard 280-day (40-week) pregnancy estimate used in obstetric dating, adjusted for your own cycle where relevant.
Formula: From last period: due date = last period start + 280 days + (cycle length − 28); estimated conception = last period start + 14 days + (cycle length − 28). From conception date: due date = conception date + 266 days; last period (derived) = conception date − 14 days. From IVF transfer: due date = transfer date + (266 − embryo age in days at transfer); conception (derived) = transfer date − embryo age. Trimester today is First if gestational age is under 98 days (under 14 weeks), Second if under 196 days (under 28 weeks), otherwise Third.
- Estimate from — whether you’re calculating from your last period, a known conception date, or an IVF transfer date.
- First day of last period — the start date of your last menstrual period, used in the last-period mode.
- Average cycle length — optional, in days (defaults to 28, valid range 20–45); shifts the estimate for cycles longer or shorter than 28 days.
- Conception date — the known or estimated date of conception, used in conception mode.
- Embryo transfer date — the date of embryo transfer, used in IVF mode.
- Embryo age at transfer — day 5 (blastocyst) or day 3, which changes how many days are added to the transfer date.
Example Scenarios
| Estimate from | Date entered | Detail | Estimated due date |
|---|---|---|---|
| Last period | Jan 1, 2026 | 28-day cycle | Oct 8, 2026 |
| Last period | Jan 1, 2026 | 35-day cycle | Oct 15, 2026 |
| Conception date | Feb 1, 2026 | — | Oct 25, 2026 |
| IVF transfer | Mar 10, 2026 | Day 5 blastocyst | Nov 27, 2026 |
| IVF transfer | Mar 10, 2026 | Day 3 embryo | Nov 29, 2026 |
Due Date Calculator FAQ
How does the due date change if my cycle isn’t 28 days?
The calculator adds the difference between your average cycle length and 28 days to the standard 280-day estimate. A 35-day cycle, for example, shifts the due date about a week later than a 28-day cycle would, since ovulation likely happened later in that cycle.Why do the last-period and conception methods give slightly different logic?
Gestational age is conventionally measured from the last period, which is roughly two weeks before conception for an average cycle. Calculating from a known conception date instead adds 266 days rather than 280, because it skips those first two weeks.How is my estimated conception date worked out?
From your last period, conception is estimated at 14 days after your period start, adjusted by the same cycle-length offset used for the due date. It’s an approximation based on typical ovulation timing, not a confirmed conception date.Why does day 5 vs day 3 IVF transfer change the due date?
A day-5 blastocyst is already 5 days past conception at transfer, and a day-3 embryo is 3 days past conception, so the calculator subtracts that many days from the transfer date to estimate conception before adding the standard 266 days to it.How accurate is an estimated due date?
It’s a general estimate, not a guarantee — only a small share of babies arrive on their exact estimated date, and most arrive within a couple of weeks of it either way. A dating ultrasound with your doctor or midwife is more accurate, especially with irregular cycles.What do “how far along” and trimester mean on this calculator?
They show your gestational age in weeks and days counted from your (entered or derived) last period date, and which trimester that falls into. This is for general information only — your antenatal care team can confirm your dates and stage of pregnancy.Related Calculators
If you’re trying to conceive rather than already expecting, the ovulation calculator for finding your fertile window uses the same cycle inputs to help with timing. Once you have a due date, the pregnancy calculator for tracking weeks and trimester can show your ongoing progress, and anyone estimating from a fertility clinic transfer date may prefer the IVF due date calculator for a more IVF-specific breakdown.