Calculate Your Estimated Due Date & Pregnancy Week
Enter the first day of your last period (LMP), your average cycle length, and the date you want to calculate from.
How this due date calculator works
This pregnancy due date and week calculator estimates your expected delivery date using the first day of your last menstrual period (LMP). The standard medical method assumes a 28-day cycle and a 40-week pregnancy (280 days). If your cycle is longer or shorter, the estimate is adjusted.
For example, if your cycle is usually 30 days, ovulation may happen a bit later than average, so the tool shifts the due date slightly forward. If your cycle is shorter, it may shift earlier.
What you get instantly
- Estimated due date (EDD)
- Current gestational age in weeks and days
- Current trimester
- Estimated conception date
- Milestone dates (end of trimesters and full-term start)
Understanding pregnancy weeks
Pregnancy weeks are counted from your LMP, not from the day of conception. That means you are considered about 2 weeks pregnant around ovulation and conception in a typical cycle.
So if the calculator says you are 10 weeks pregnant, it refers to gestational age (the clinical standard), which is what OB/GYN clinics and ultrasound reports use.
Trimester guide
- First trimester: Week 1 to week 13
- Second trimester: Week 14 to week 27
- Third trimester: Week 28 to delivery
How accurate is an estimated due date?
A due date is an estimate, not a guarantee. Most babies do not arrive on the exact date. Many are born within a window of about 1 to 2 weeks before or after the estimate.
Early ultrasound dating can be more accurate than LMP dating, especially if:
- Your cycles are irregular
- You are unsure of your LMP date
- You conceived soon after stopping hormonal contraception
- Your provider sees a significant difference between LMP and ultrasound measurements
When to use this pregnancy week calculator
This tool is useful for planning and tracking milestones like:
- First prenatal appointment timing
- NIPT and screening windows
- Anatomy scan scheduling
- Maternity leave and work planning
- General week-by-week progress tracking
Tips for more reliable results
1) Enter the exact first day of your period
This is the most important input. If you are unsure, check your cycle app or calendar history.
2) Use your typical cycle length
If your cycles vary, choose your average over the last few months rather than one unusual cycle.
3) Re-check after your ultrasound
Your care team may update your due date based on early ultrasound findings. Use that date for all medical planning.
Frequently asked questions
Can I calculate due date from conception date instead of LMP?
Yes, but this calculator is LMP-based because that is the most common clinical standard. If you know the exact conception date, a rough estimate is conception date + 266 days.
What if I have irregular periods?
Use this calculator for an initial estimate only. Early ultrasound is usually the best way to date pregnancy when cycles are irregular.
Does a due date mean labor starts that day?
Not usually. It marks 40 weeks gestation. Labor can start before or after this date and still be considered normal.
Important note
This calculator is educational and not a medical diagnosis. Always confirm dating and care decisions with your OB/GYN, midwife, or healthcare provider.