Pregnancy Due Date Calculator
Find your estimated due date, current pregnancy week and key milestones — calculated from your last period, conception date, or a known due date. Free, instant, based on the standard method doctors use worldwide.
How Is a Due Date Calculated?
A typical pregnancy lasts approximately 280 days (40 weeks) from the first day of your last menstrual period (LMP). This method, known as Naegele's Rule, is the standard calculation used by doctors and midwives worldwide.
If your menstrual cycle is longer or shorter than the standard 28 days, the calculator adjusts your estimated due date accordingly, since ovulation timing shifts with cycle length.
Pregnancy Trimesters Explained
| Trimester | Weeks | What's Happening |
|---|---|---|
| First Trimester | Weeks 1–13 | Major organ development, morning sickness common |
| Second Trimester | Weeks 14–27 | Often called the "easier" trimester, baby movements begin |
| Third Trimester | Weeks 28–40 | Rapid weight gain, preparation for birth |
| Full Term | Weeks 39–40 | Baby is considered full term and ready for birth |
Three Ways to Calculate Your Due Date
- From Last Menstrual Period (LMP). The most common method, using the first day of your last period as the starting point. This is what most doctors use at your first prenatal appointment.
- From Conception Date. If you know roughly when conception occurred (useful for IVF or if you track ovulation), this method calculates 266 days from that date instead.
- From a Known Due Date. If your doctor has already confirmed a due date via ultrasound, enter it directly to see your current week and key milestones without recalculating.
Key Pregnancy Milestones
Why Due Dates Aren't Exact
A due date is an estimate based on average pregnancy length, but every pregnancy is different. Factors that can affect actual delivery timing include cycle length variation, when ovulation actually occurred versus assumed timing, and individual differences in gestation length. This is why doctors often describe a due date as an estimated date rather than a fixed appointment — and why ultrasound dating in early pregnancy is generally considered more accurate than calculation from last period alone if the two dates differ significantly.
FAQs
How accurate is this due date calculator?
It uses Naegele’s Rule, the standard medical method. Most babies arrive within 2 weeks either side of the due date — only around 5% are born exactly on their due date.
What if I don't know my last period date?
Use the Conception Date option if you know roughly when conception occurred, or the Known Due Date option if your doctor has already given you one.
What week am I in my pregnancy?
Enter your last period date and the calculator will show your exact current week and day of pregnancy.
What is the difference between LMP and conception dating?
LMP (last menstrual period) dating counts 280 days from your last period. Conception dating counts 266 days from the actual conception date. Both should give a similar due date if your cycle is close to 28 days.
How accurate is ultrasound dating compared to this calculator?
Early ultrasound dating (typically 8-13 weeks) is generally considered slightly more accurate than calculation from last period alone, especially if your cycle is irregular. If your doctor’s ultrasound date differs from this calculator, the ultrasound date usually takes priority.
What if my cycle isn't exactly 28 days?
A shorter cycle typically means ovulation happens earlier, which can shift your due date slightly earlier. A longer cycle shifts it later. This calculator’s Last Period method uses the standard 28-day assumption — the Conception Date method is more precise if you know your actual ovulation timing.
Is this calculator free?
Yes, completely free with no sign-up required.