How accurate is a pregnancy due date calculator?

It gives a good starting estimate, but only about 5% of babies arrive exactly on the predicted date. Most births happen within two weeks either side of the EDD. An early ultrasound scan (8–14 weeks) is more accurate than LMP alone, especially if your cycle is irregular.

What is the first day of my last period?

It's the very first day you noticed bleeding in your most recent menstrual cycle — not the last day, and not the day before spotting started. If you're unsure, use your best estimate; your dating scan will fine-tune things.

What if my cycle isn't 28 days?

Enter your actual average cycle length (anywhere from 21 to 35 days is normal). The calculator shifts the due date forward or back by the same number of days your cycle differs from 28. A 35-day cycle pushes the EDD about 7 days later, for example.

Can I use this calculator for IVF pregnancies?

Not reliably. IVF due dates are calculated differently — from the egg retrieval date or embryo transfer date — and your fertility clinic will give you a precise EDD. This LMP-based tool is designed for natural cycles.

Is my data saved or uploaded anywhere?

No. The entire calculation happens inside your browser. The date you enter is never sent to any server, stored in a database, or shared with anyone. You can even use it offline once the page has loaded.

What does 'gestational age' mean?

Gestational age is how many weeks and days pregnant you are, counted from the first day of your last period — not from conception. So at four weeks pregnant, the embryo has typically only existed for about two weeks.

When should I see a doctor or midwife after finding out I'm pregnant?

As soon as possible, and ideally before 10 weeks. Early appointments let your care provider arrange a dating scan, check your health, and discuss things like folic acid, diet, and any risk factors. Most healthcare systems ask you to contact your GP or midwife right away.

Is this due date calculator free to use?

Yes, completely free — no sign-up, no subscription, no hidden fees. Use it as many times as you like.

Pregnancy Due Date Calculator – Find Your EDD Free

What This Pregnancy Due Date Calculator Tells You

Enter the first day of your last menstrual period (LMP) and this calculator gives you your estimated due date — the date your baby is expected to arrive — plus how many weeks pregnant you are today. It takes about three seconds and requires just one date.

Everything runs entirely in your browser. No data is sent to any server, so your personal health information stays completely private.

How to Use the Due Date Calculator

Pick the first day of your last period. This is the date your most recent menstrual period began — not the day it ended.
Enter your average cycle length (optional). The default is 28 days, but cycles between 21 and 35 days are common. Adjusting this makes the estimate more accurate for you.
Hit Calculate. Your estimated due date, current gestational age (how far along you are), and your first trimester end date appear instantly.
Note the result is an estimate. Only about 5% of babies arrive exactly on their due date — most come within two weeks either side.

Worked Example

Suppose your last period started on 1 March 2025 and your cycle is the standard 28 days.

Estimated due date: 6 December 2025
Gestational age today (if today is 15 May 2025): 10 weeks and 2 days
End of first trimester: around 14 June 2025

If your cycle were 35 days instead of 28, the calculator shifts the estimated due date forward by 7 days to 13 December 2025, because ovulation likely happened later in your cycle.

How Your Due Date Is Calculated – Naegele's Rule

Naegele's rule is the standard method midwives and obstetricians have used for over 200 years. The idea is straightforward: pregnancy lasts about 280 days (40 weeks) from the first day of your last period.

In plain arithmetic:

Due date = LMP + 280 days

Or, using the classic shorthand formula doctors write on notepads:

Due date = LMP + 1 year − 3 months + 7 days

Worked example with the formula: LMP = 1 March 2025 → add 1 year = 1 March 2026 → subtract 3 months = 1 December 2025 → add 7 days = 8 December 2025. (A tiny rounding difference from the example above comes from February's length — calculators handle this automatically.)

If your cycle differs from 28 days, the calculator adjusts by adding or subtracting the difference:

Adjusted due date = LMP + 280 days + (your cycle length − 28 days)

Trimester	Weeks of pregnancy	Key milestones
First	Weeks 1–13	Heartbeat detectable ~week 6; nuchal scan ~week 12
Second	Weeks 14–27	Anatomy scan ~week 20; baby movements felt
Third	Weeks 28–40+	Rapid growth; lung maturity; birth

How to Read Your Result — and What It Can't Tell You

Your estimated due date (EDD) is a statistical midpoint, not a deadline. Research consistently shows fewer than 1 in 20 babies arrive on the exact predicted date. A birth between 37 and 42 weeks is considered full-term by most clinical guidelines.

This calculator uses your LMP date, which is the same starting point your midwife or OB will use at your first appointment. Once you have an early ultrasound scan (usually between 8 and 14 weeks), your care provider may adjust the EDD based on the baby's measured size — and that scan-based date is generally considered more accurate.

Things that don't affect this calculator's output but do affect your real pregnancy timeline:

Irregular periods or recently stopped hormonal contraception
Polycystic ovary syndrome (PCOS) or other conditions that affect ovulation
IVF or assisted conception (your clinic will give you a precise date based on embryo transfer)

Practical Tips for the Weeks Ahead

Book your first antenatal appointment early. Most guidelines recommend seeing a midwife or GP before 10 weeks. They'll confirm the pregnancy, check your health history, and arrange your dating scan.

Start (or continue) folic acid. A daily 400 mcg folic acid supplement is recommended from before conception through the first 12 weeks to support the baby's neural tube development. Your doctor or midwife can advise on the right dose for you.

Track your symptoms, but don't panic. Nausea, fatigue, and breast tenderness are very common in early pregnancy. If you have significant pain or heavy bleeding, contact your care provider promptly.

Note your cycle history. Jot down the dates of your last two or three periods before your first appointment — it helps your midwife confirm how far along you are.

For evidence-based guidance on prenatal care, the WHO antenatal care recommendations and the NHS Pregnancy guide are reliable, plain-language resources.

This calculator is for educational and planning purposes only — it is not medical advice. Your midwife or obstetrician is the right person to confirm your due date, monitor your pregnancy, and answer any clinical questions.

Ready to find your estimated arrival date? Use the calculator at the top of the page — it takes seconds and your information never leaves your device.

Pregnancy Due Date Calculator – Find Your Baby's Arrival Date

Pregnancy details