Pregnancy Calculator
Due date = LMP + 280 days (Naegele's rule)Jan 15 + 280 days ≈ Oct 22, 2026
Free online tool
Pregnancy Calculator
Enter the first day of your last menstrual period to estimate your due date and track your pregnancy week.
Instant calculation
Calculate Due Date
Enter the date of your last period.
Your result
Calculation
Your numbers stay in this browser. Nothing is uploaded or saved.
Three clear steps
How to use this calculator
- 01
Enter LMP date
Type the first day of your last menstrual period.
- 02
Calculate
See your estimated due date.
- 03
Track your week
The calculator also shows your current pregnancy week and trimester.
The formula
How this calculation works
Add 280 days (40 weeks) to the first day of your last menstrual period. This is Naegele's rule, the standard method for estimating due dates.
Check the method
Worked examples
Each example follows the same formula used by the calculator.
LMP Jan 15, 2026 — when is the due date?
Jan 15 + 280 days ≈ Oct 22, 2026≈ October 22, 2026Common questions
Questions about this calculation
What is the Pregnancy Calculator?
The Pregnancy Calculator helps you calculate your estimated due date and current pregnancy week from your last period. Enter your values and select Calculate to get an instant result.
How is the result calculated?
Add 280 days (40 weeks) to the first day of your last menstrual period. This is Naegele's rule, the standard method for estimating due dates.
Can you show an example?
Example: LMP Jan 15, 2026 — when is the due date? — ≈ October 22, 2026.
Is my data saved when I use the Pregnancy Calculator?
No. All calculations run locally in your browser. Your inputs and results are never uploaded, stored or shared with anyone.
Is the Pregnancy Calculator free to use?
Yes. The Pregnancy Calculator is completely free. No account, sign-up or payment is required. It works on mobile, tablet and desktop.
Continue calculating