What it calculates
Pregnancy is conventionally counted from the first day of the last menstrual period, about two weeks before conception. This calculator uses that convention.
How it works
The calculator adjusts the start date for cycles longer or shorter than 28 days, then counts weeks and days to today.
Formula
Weeks pregnant = (Today − Adjusted LMP) ÷ 7
- Adjusted LMP = LMP + (cycle length − 28) days
How to use it
- Enter the first day of your last period.
- Enter your usual cycle length.
- Read your estimate and the key dates table.
For a period that started 10 weeks ago with a 28-day cycle:
Why it helps
- Quick estimate of stage and trimester.
- Shows upcoming milestones.
Limitations
- Irregular cycles make date-based estimates less reliable.
- An ultrasound dating scan is the usual confirmation.
Frequently asked questions
Why am I “two weeks pregnant” at conception?
Because pregnancy is counted from the last period, not from conception.
Do you store what I enter?
No. This calculator runs entirely in your browser. Your measurements and dates are not sent to or stored on our servers.
Sources
These calculators provide estimates only and are not a substitute for medical advice. Dates and ranges vary between individuals; follow the guidance of your doctor or midwife. Your inputs stay in your browser and are not stored by UrbanFiling.