Due Date Calculator
Find your baby's estimated due date from your last period, conception date, or IVF transfer.
Due Date Calculator
Estimate your baby's due date
Based on last menstrual period
Due date = LMP + 280 daysWhat Is a Due Date Calculator?
A due date calculator estimates when your baby is likely to arrive based on one of three methods: your last menstrual period (LMP), your known conception date, or your IVF embryo transfer date. The most common method — the Naegele Rule — adds 280 days (40 weeks) to the first day of your last period. This assumes a standard 28-day cycle, so the calculator lets you adjust for longer or shorter cycles to get a more personalized estimate.
Keep in mind that a due date is always an estimate. Statistically, only about 4% of babies are born on their exact calculated due date. The full-term range spans from 37 to 42 weeks of gestation, and many healthy babies arrive a week or two before or after the predicted date. Your healthcare provider may revise the due date after a first-trimester ultrasound, which measures fetal size and is often more precise than LMP dating — especially if your cycles are irregular.
How to Use This Calculator
- 1Select your calculation method: Last Menstrual Period (LMP), Conception Date, or IVF Transfer Date.
- 2Enter the relevant date — the first day of your last period, the date of conception, or your embryo transfer date.
- 3If using the LMP method, enter your average cycle length (default is 28 days) to improve accuracy.
- 4Click Calculate to instantly see your estimated due date, current gestational age in weeks, and which trimester you are in.
Due Date Formulas
From LMP (Naegele Rule):
Due Date = LMP + 280 days
Due Date = LMP + 9 months + 7 days
From Conception Date:
Due Date = Conception + 266 days (38 weeks)
From IVF Transfer (Day 5 blastocyst):
Due Date = Transfer date + 261 days
From IVF Transfer (Day 3 embryo):
Due Date = Transfer date + 263 days
Gestational age = (Today − LMP) ÷ 7 weeksDue dates may be adjusted by your healthcare provider after an ultrasound measurement. First-trimester ultrasounds (crown-rump length) are generally more accurate than LMP dating and are the gold standard when the two methods disagree by more than 5–7 days.
Worked Examples
Example 1 — LMP Method (28-day cycle)
Last menstrual period: February 1. Adding 280 days gives an estimated due date of November 8. At 10 weeks of pregnancy, a fetal heartbeat is typically detectable via transvaginal ultrasound, and the embryo has developed all major organ systems.
Example 2 — Conception Date Method
Known conception date: March 20. Adding 266 days (38 weeks from conception) gives an estimated due date of December 11. At 12 weeks, the pregnancy has reached the end of the first trimester — the period of highest miscarriage risk is now behind you, and the baby is fully formed and growing rapidly.
Example 3 — Day-5 IVF Blastocyst Transfer
Embryo transfer date: April 1 (Day 5 blastocyst). Adding 261 days gives an estimated due date of December 19. Because the exact fertilization age of the embryo is known, IVF due dates are often more reliable than LMP-based estimates.