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Pregnancy Due Date Calculator

Estimate baby due date from last menstrual period and typical cycle length using calendar math.

By UtilityKit Team · Reviewed for accuracy by UtilityKit Editors · Updated May 2026

About Pregnancy Due Date Calculator

Knowing your estimated due date is the first milestone of pregnancy — it anchors every subsequent appointment, trimester boundary, and baby-product delivery window. This calculator uses Naegele's Rule (LMP + 280 days) to compute your Estimated Due Date. If your cycle differs from 28 days, the tool adjusts automatically for your actual ovulation timing. You can also enter a known conception date or an IVF transfer date for a more direct calculation. Once the EDD is set, the tool maps all three trimester boundaries, shows how many weeks and days pregnant you are today, and counts the days remaining. All dates are computed in your browser and never transmitted to any server — sensitive health information stays private. Only about 5% of births occur on the exact due date; full term is 37 to 42 weeks.

Why use Pregnancy Due Date Calculator

Naegele's Rule

Uses the standard LMP + 280 days clinical formula, identical to what most obstetricians apply at first appointments. The calculation is recognised by major health bodies worldwide and gives a reliable baseline before ultrasound confirmation.

Trimester Map

Automatically shows the start and end dates of all three trimesters based on your EDD. No guessing which week a trimester begins — the boundaries are displayed clearly alongside your current position in the pregnancy.

Conception Date Mode

Switch from LMP to a known conception date or an IVF embryo transfer date for a more direct calculation. IVF patients have precise transfer dates that eliminate the uncertainty inherent in cycle-based estimates.

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 EDD — approximately four days later, and the tool handles this automatically.

Weeks-pregnant Now

Displays your current gestational age in weeks and days updated to today's date. This live count matches the week references used in most pregnancy books, apps, and medical charts.

Privacy First

Health and reproductive data is especially sensitive. Every date entered is computed locally in your browser and never sent to a server, stored in a database, or used for any analytics purpose.

How to use Pregnancy Due Date Calculator

Select an input method: last menstrual period (LMP), known conception date, or IVF transfer date.
Enter the date using the calendar picker or type it in YYYY-MM-DD format.
Adjust the average cycle length if your cycle is not the assumed 28 days.
Read your Estimated Due Date and the current week and days of pregnancy.
Review the trimester boundaries — when each trimester starts and ends.
Note the days remaining to your EDD for planning appointments and purchases.

When to use Pregnancy Due Date Calculator

Getting a quick EDD 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.
Calculating the EDD from a confirmed conception or ovulation date rather than LMP.
Finding exact trimester boundaries for planning travel, work, or baby-shower timing.
Checking current gestational age in weeks when a medical chart references week numbers.

Examples

LMP method

Input: LMP: 2026-02-01, Cycle: 28 days

Output: Due date: 2026-11-08, Currently: 13 weeks, 3 days

Conception date

Input: Conception: 2026-02-15

Output: Due date: 2026-11-08, T1 ends: 2026-04-26

Long cycle

Input: LMP: 2026-02-01, Cycle: 32 days

Output: Due date: 2026-11-12 (4-day push for cycle length)

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

How accurate is the due-date estimate?▾

LMP-based estimates are accurate to within ±2 weeks for most pregnancies. Only about 5% of babies are born on the exact calculated due date. A dating ultrasound at 8–12 weeks is more accurate and will often adjust the EDD.

What is Naegele's Rule?▾

Naegele's Rule calculates the EDD by adding 280 days (40 weeks) to the first day of the last menstrual period, then subtracting three months and adding seven days. The net result is the same: LMP + 280 days.

How does cycle length change my due date?▾

The 280-day formula assumes ovulation on day 14 of a 28-day cycle. If your cycle averages 32 days, ovulation likely occurs around day 18, pushing the EDD approximately 4 days later. The tool adds this offset automatically.

What's the difference between gestational age and fetal age?▾

Gestational age counts from the first day of the LMP and is what doctors and apps report. Fetal age counts from actual conception, which is roughly two weeks less. Medical charts always use gestational age.

When do trimesters start and end?▾

Standard boundaries: the first trimester covers weeks 1–12, the second covers weeks 13–26, and the third covers weeks 27 through birth. Some sources use 13/14 and 27/28 as the cutoff weeks — minor variation exists.

Why do only ~5% of babies arrive on the exact due date?▾

The due date is a statistical midpoint, not a precise target. Normal term runs from 37 to 42 weeks, and most births cluster in a two-week window around the EDD rather than on the exact date.

Can ultrasound override the LMP-based due date?▾

Yes. A first-trimester dating ultrasound (8–12 weeks) measures the embryo's crown-rump length, which is more accurate than LMP dating. Clinicians typically adjust the EDD if the ultrasound date differs by more than 5–7 days.

How does IVF transfer date affect the calculation?▾

For IVF, gestational age is counted from a standardised reference: 2 weeks before a day-3 transfer, or 2 weeks before a day-5 (blastocyst) transfer. Enter the transfer date and cycle day in the IVF mode and the tool computes the offset.

Explore the category

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.