Pregnancy Week

Pregnancy Week — runs in your browser. Inputs are not stored.

Runs in your browser No sign-up Free to use

Pregnancy week (for reference)

Last menstrual period start (LMP)

Reference date (today if empty)

Enter values, then press Calculate.

How to use

Pick last menstrual period start (LMP) on the calendar. It is the day bleeding started, not ovulation day.
Reference date defaults to today. Change it to see gestational age on a specific date.
Press Calculate for gestational age (weeks + days) and due-date D-day. The due date is LMP + 280 days.
If this differs from ultrasound or the obstetric clinic’s weeks, the hospital record takes priority. This screen is obstetric reference only.
A future date, or an LMP after the reference date, shows an error. This is not medical advice.

Key concepts

The pregnancy week calculator is used to find how many weeks, LMP dating, and due-date D-day. A common obstetric method is days since LMP start divided by 7 as weeks + days. The due date is LMP plus 280 days, like Naegele. There is no ovulation-day mode.

Late ovulation or implantation can diverge from true embryo age. Irregular cycles and assisted reproduction may match ultrasound dating better. This is not diagnosis or medical advice and can differ from ultrasound. Dates are calculated in the browser only. If you have irregular cycles, ART, or ultrasound weeks, follow the hospital record.

Example

LMP 2026-01-01 and reference 2026-03-01 is 59 days elapsed, shown as 8 weeks 3 days. The due date is around 2026-10-08 (LMP + 280 days), and D-day is days remaining from the reference date to that date. If hospital ultrasound says 7 weeks, follow the hospital weeks. LMP 2026-02-01 and reference 2026-04-01 is about 8 weeks 3 days. The due date is shown with D-day as LMP + 280 days.

Notes

This result is not medical diagnosis or treatment advice. Decide health, pregnancy, and nutrition matters with a clinician. Pregnancy weeks and due date are for reference and do not replace care.

Frequently asked questions

How is the due date calculated from LMP?

LMP + 280 days (Naegele). Follow the hospital’s judgement for the actual birth date. The 280-day Naegele assumption can drift with cycle length.

If ovulation day is exact, is gestational age more accurate?

This tool is LMP-based. There is no ovulation-day mode. Even if you enter ovulation day, only LMP is used.

Are pregnancy-week inputs sent to a server?

No. Dates are counted in the browser only.

If this differs from hospital ultrasound weeks, which do I follow?

Follow the hospital. This number is for reference. A few days’ difference from ultrasound is common; follow clinical care.

Is the pregnancy week calculator medical?

No. It is obstetric reference only, not a diagnosis. It is not for medical use.

If I leave the reference date empty, is today used?

Yes. An empty reference date uses today. The screen may also pre-fill today’s date.

Your input is not sent to the server and disappears when you close the page.

Last reviewed: 2026-09-04