Date Estimator
Pregnancy

Pregnancy Due Date Calculator

Enter the first day of your last menstrual period and your average cycle length. The calculator uses Naegele's rule (LMP + 280 days) and adjusts for cycle length to estimate your due date, conception date, trimesters and current pregnancy week.

Your information

The first day of bleeding, not the last.
Most people are between 21 and 35 days.

Tip: if you know your conception date instead, try our Conception Date Calculator.

Your estimate

Estimated due date —
Estimated conception date—
Current week of pregnancy—
Trimester—
Days remaining—
Day of the week (due date)—

Key milestones

    Heads up: Only about 4% of babies are born on their estimated due date. About 80% arrive within two weeks of it. Always confirm pregnancy dating with your healthcare provider.

    How the pregnancy due date calculator works

    Pregnancy is dated from the first day of the last menstrual period (LMP), not from the day of conception. This convention exists because most people know the date of their last period, while the exact moment of fertilization is rarely observable. The standard calculation — known as Naegele's rule — assumes a textbook 28-day cycle with ovulation on day 14:

    Estimated Due Date (EDD) = First day of LMP + 280 days (40 weeks)

    When your cycle is shorter or longer than 28 days, the calculator adjusts by the difference. For example, on a 32-day cycle, the EDD is shifted four days later because ovulation happens four days later.

    What the timeline looks like

    StageWeeks from LMPWhat's happening
    First trimester0 – 13 weeksMajor organs form. Highest sensitivity to medications and infections.
    Second trimester14 – 27 weeksBaby grows rapidly. First movements ("quickening") usually felt 18–22 weeks.
    Third trimester28 – 40 weeksLungs mature, weight gain accelerates, baby moves into birth position.

    What the milestones mean

    • End of week 12: Generally the end of the highest-risk window for miscarriage.
    • Week 20: The mid-pregnancy anatomy ("anomaly") scan is typically scheduled around this time.
    • Week 24: Considered the threshold of viability in most countries.
    • Week 28: Start of the third trimester. Glucose screening is common.
    • Week 36: Full-term considerations begin. Group B strep screening is typical.
    • Week 40: Estimated due date.

    FAQ

    Is the due date the same as the birth date?
    No — only ~4% of births occur on the exact estimated due date. Most fall within a 38-to-42-week window.
    Should I use the LMP date or an ultrasound date?
    If you've had an early ultrasound (before week 14), its dating is typically more accurate than LMP-based dating. After 14 weeks, LMP and ultrasound dates usually align closely.
    Can I use this calculator for IVF pregnancies?
    For IVF, your clinic will give you a precise transfer or retrieval date. This calculator assumes a natural cycle. For IVF, count 266 days from retrieval, or 261 days from a day-5 transfer.
    What if my periods are irregular?
    If you don't have a reliable LMP, an early ultrasound is the most accurate way to date a pregnancy. The calculator's estimate becomes less reliable as cycle variability increases.

    Medical disclaimer: This calculator is for informational purposes only and does not replace medical advice. Confirm pregnancy dating with your doctor or midwife.