Everyday
Pregnancy Weeks Calculator
Calculate estimated gestational age in weeks and days on a chosen date. Change the inputs below and the estimate updates immediately.
Women’s health · calendar estimates
Use your clinician’s confirmed pregnancy dating for medical decisions. This estimate cannot confirm pregnancy or predict the exact day of birth.
Your calculator inputs stay in this page and are not saved or sent to us.
Input
Your numbers
Calculated result
Estimated gestational age
4 weeks, 0 days
Counted from the first day of your last period.
Unadjusted estimated due date
June 21, 2027
Days until estimated due date
252 days
Calendar estimate, not a prediction of the day of birth.
Estimate only. Verify important decisions with an appropriate professional or official source.
How to use it
A quick estimate, without the spreadsheet.
Inputs and units
Enter the first day of your last menstrual period and the date on which you want to estimate gestational age. The assessment date must be on or after the period date; this tool supports up to 45 weeks for arithmetic only.
Formula
Gestational days = assessment date − last menstrual period date. Completed weeks = whole days ÷ 7 rounded down; remaining days = the remainder. The unadjusted due date is last period + 280 days.
Worked example
From January 1 to April 1, 2026 is 90 days, so estimated gestational age is 12 weeks and 6 days. The unadjusted due date is October 8, 2026.
Assumptions and limitations
An estimated due date is not a promised birth date. Uncertain period dates, irregular cycles and fertility treatment can change pregnancy dating. Use the date confirmed by your maternity clinician or dating ultrasound for medical decisions. These tools do not assess fetal development or diagnose pregnancy. Gestational age is counted from the last period, usually about two weeks before conception; it is not time since conception. This tool assumes a 28-day cycle and does not replace clinical dating. The 45-week input limit does not describe a safe pregnancy duration.
Health references
Keep calculating