Free online calculator
Due Date Calculator
Estimate due date from last menstrual period or conception date using standard rules.
Quick Answer
How It Works
LMP method adds 280 days to period start. Conception method adds 266 days to conception date.
- Choose LMP or conception method.
- Enter the relevant date.
- Read estimated due date and gestational week count.
Examples use USD-style formatting. Tax rates, fees, and legal rules vary by country and change over time — treat results as estimates and confirm important numbers with a qualified professional.
Interactive Calculator
Estimated due date: 2027-05-01
Example Use Case
If LMP starts on January 1, estimated due date is around October 8.
Detailed Guide
Due-date estimation is useful for planning milestones, but biological variation means outcomes are approximate.
Cycle uncertainty and irregularity can materially shift predicted timelines compared with clinical dating methods.
Use this calculator for orientation and scheduling context rather than medical decision-making.
For final guidance, users should confirm timelines with healthcare professionals.
Assumptions and Limits
This is an estimate only and not a substitute for medical guidance or ultrasound-based dating.
Common Mistakes to Avoid
- Using uncertain or approximate cycle dates as exact input.
- Assuming every cycle length is 28 days.
- Treating estimate as medical diagnosis.
FAQ
Can I use this calculator for free?
Yes. This tool is free and designed for practical day-to-day decisions.
Why might results differ from another website?
Differences usually come from rounding rules, assumptions, or region-specific formulas.
Is this suitable for legal or financial advice?
No. Treat outputs as guidance and validate with qualified professionals for final decisions.
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How we choose formulas and check results: Methodology · Last reviewed 2026-07-25