LMP Calculator (Last Menstrual Period Calculator)
Want to calculate your due date instead? Try the Due Date Calculator.
How to Use the LMP Calculator
- Enter your estimated due date.
- Click Calculate LMP.
- The tool subtracts 280 days (40 weeks) from your due date.
- Your estimated LMP date appears instantly.
This calculator is helpful for anyone wanting to quickly figure out:
- “When did my last period start?”
- “How do I calculate LMP from my due date?”
- “What was the start date of my pregnancy?”
Everything is based on simple date math.
FAQ
How is the LMP calculated?
The calculator subtracts 280 days (40 weeks) from your due date. This is the standard method used for estimating the start of pregnancy using date math.
Why 280 days?
Because pregnancy dating traditionally uses a 40 week model that begins on the first day of the LMP.
Is this the same as calculating conception?
No. Conception typically occurs about 14 days after the LMP.
This tool calculates the LMP, not the conception date.
Does this give a medically verified LMP?
No — this is a date math calculator only, not medical advice. It simply subtracts 280 days from your due date.
Can this help with pregnancy timelines?
Yes. Many people use this tool for:
- “LMP from due date calculator”
- “pregnancy start date calculator”
- “last menstrual period date estimator”
It’s a quick way to map out the beginning of the pregnancy timeline.