Pregnancy Due Date Calculator — LMP, Conception or IVF
Estimate your due date from your last menstrual period (adjusted for cycle length), conception date or IVF transfer, and see how far along you are with key prenatal milestones and term dates.
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Your Pregnancy Timeline
Dates for common prenatal milestones based on your estimated due date. Your care team sets your actual schedule.
| Milestone | Gestational Age | Date |
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How this calculator works
- Last menstrual period (Naegele's rule): due date = first day of LMP + 280 days (40 weeks). For cycles other than 28 days, the calculator adds or subtracts the difference (e.g. +2 days for a 30-day cycle), since ovulation shifts with cycle length.
- Conception date: due date = conception + 266 days (38 weeks).
- IVF transfer: due date = transfer date + 266 days − embryo age (263 days for a day-3 transfer, 261 for day 5, 260 for day 6).
Gestational age is counted from the first day of the LMP, so at conception you are already about 2 weeks pregnant. Trimesters: first up to 13 weeks 6 days, second 14w0d–27w6d, third from 28 weeks.
By Suhaib Hassan · Reviewed 28 September 2026 against ACOG guidance · How CalculatePilot verifies formulas →
A worked example
A last period starting 1 March 2026 with a 28-day cycle: 1 March + 280 days = 6 December 2026. With a 32-day cycle the estimate moves 4 days later, to 10 December. A day-5 IVF transfer on 15 March 2026 gives 15 March + 261 days = 1 December 2026.
How accurate is a due date?
Relatively few babies arrive exactly on their due date — most are born within a couple of weeks either side. The American College of Obstetricians and Gynecologists (ACOG) considers an ultrasound in the first trimester the most accurate way to date a pregnancy, and your provider may change your due date if the scan and your LMP date differ by more than a set number of days. IVF dates are the most precise because the embryo's age is known.
ACOG term definitions: early term 37w0d–38w6d, full term 39w0d–40w6d, late term 41w0d–41w6d, and post-term from 42w0d. This is information, not medical advice — your care team confirms your dates and schedule.
Sources
- ACOG Committee Opinion No. 700 — Methods for Estimating the Due Date (2017)
- ACOG Committee Opinion No. 579 — Definition of Term Pregnancy (2013)
- ACOG Practice Bulletin No. 175, Ultrasound in Pregnancy (2016) — standard anatomy exam at 18–22 weeks.
- ACOG Practice Bulletin No. 190, Gestational Diabetes Mellitus (2018) — screening at 24–28 weeks.
- ACOG Committee Opinion No. 797, Prevention of Group B Streptococcal Early-Onset Disease in Newborns (2020) — screening at 36w0d–37w6d.
Read the guide: How do you calculate your due date? LMP, conception and IVF
Frequently asked questions
Why is pregnancy counted from my last period, not conception?
The first day of the last period is usually a known date, while conception usually isn't. Counting from the LMP adds about two weeks before conception, which is why a full-term pregnancy is described as 40 weeks.
What if my cycles are irregular?
LMP-based dates are less reliable with irregular or unknown cycles. An early ultrasound gives a more accurate estimate, and your provider will usually date the pregnancy from it.
Can my due date change?
Yes. If an early ultrasound measurement differs from your LMP date by more than ACOG's thresholds, your provider may update your due date. Once set from an early scan, it usually isn't changed by later scans.
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