Pregnancy Due Date Calculator

About this tool

Knowing your estimated due date is the first milestone of pregnancy — it anchors appointments, trimester planning, and maternity-leave paperwork. This calculator uses Naegele's Rule (first day of your last menstrual period + 280 days) to estimate your due date. If your average cycle differs from 28 days, it shifts the estimate by the difference — a 32-day cycle moves the date four days later — and you can enter any cycle from 21 to 45 days. Click Calculate to see the estimated due date, a rough conception date (about two weeks after the LMP, adjusted for cycle length), how many whole weeks have passed since your LMP, which trimester you are in today, and the days left until the due date. All dates are computed in your browser and never transmitted to any server. It is an educational estimate, not medical advice: only about 5% of births occur on the exact due date, and full term is 37 to 42 weeks.

Why use it

• Naegele's Rule: Uses the standard LMP + 280 days formula that most clinicians apply at a first appointment, giving a familiar baseline before ultrasound confirmation.

• Cycle-length Aware: Adjust your average cycle length from the default 28 days to account for longer or shorter cycles. A 32-day cycle pushes ovulation — and therefore the due date — about four days later, and the tool applies this automatically.

• Rough Conception Date: Shows the likely conception window (ovulation day) implied by your LMP and cycle length, which is useful when comparing with a known date.

• Where You Are Today: Displays weeks since LMP, the current trimester and the days remaining until the due date, all counted to today's date.

• Privacy First: Health and reproductive data is especially sensitive. Every date entered is computed locally in your browser and never sent to a server or stored.

How to use

1. Enter the first day of your last menstrual period (LMP) in the date picker
2. Adjust Avg cycle (days) if your cycle is not the default 28 days — any value from 21 to 45
3. Click Calculate
4. Read your estimated due date and the rough conception date
5. Check weeks since LMP, your current trimester and the days left until the due date

When it helps

• Getting a quick due-date estimate before your first prenatal appointment to plan maternity leave paperwork.
• Verifying that the due date your midwife quoted matches Naegele's Rule calculation.
• Adjusting the estimate when your cycle length differs from the standard 28-day assumption.
• Checking how many weeks have passed since your LMP when a chart references week numbers.
• Counting the days left until the due date for planning work, travel, or a baby shower.

Examples

Tips

• Confirm the LMP-based estimate at your 8–12 week dating ultrasound — Crown-rump length measurement is more precise than cycle math.
• If your cycles vary widely in length, use the average from your last 3 cycles rather than the default 28 days.
• Trimester boundaries vary slightly by source; always use your provider's definition for medical decisions.
• Track current week each Monday — most pregnancy books, apps, and medical charts reference week numbers, not exact dates.
• An estimated due date is not a deadline — normal full-term delivery happens anywhere between 37 and 42 weeks.

Frequently Asked Questions

Glossary

LMP (Last Menstrual Period)

The first day of the most recent menstrual period before conception. LMP is the standard reference point for calculating gestational age and estimated due date because conception date is rarely known with certainty.

EDD (Estimated Due Date)

The projected date of delivery calculated as 280 days (40 weeks) from the LMP. The EDD is a statistical estimate — most births occur within two weeks before or after this date.

Naegele's Rule

A standard obstetric formula for calculating EDD: take the first day of the LMP, subtract three months, and add one year and seven days. The net result equals LMP plus 280 days.

Gestational Age

The age of a pregnancy measured in weeks and days from the first day of the LMP. Gestational age is always about two weeks more than the actual fetal age from conception, and it is the standard used in medical charts.

Trimester

One of three roughly equal stages of pregnancy. The first trimester spans weeks 1–12, the second weeks 13–26, and the third weeks 27 through delivery. Each trimester carries distinct developmental milestones and medical checkpoints.

Ovulation

The release of an egg from the ovary, typically occurring around day 14 of a 28-day cycle. Conception requires fertilisation within 12–24 hours of ovulation. Cycle-length adjustments in due-date calculators estimate the actual ovulation day.