Due Date Calculator
Multi-Method Due Date Estimator
Choose the dating method that applies to you for the most accurate estimate.
Parameters
Estimated Due Date
Understanding Due Date Methods
There's more than one way to estimate a due date. This calculator supports the five most common dating methods, each useful in different situations — from a standard LMP-based estimate to precise IVF transfer dating.
LMP-Based (Naegele's Rule)
The most common method: 280 days from the first day of your last period. Assumes a standard 28-day cycle.
Conception-Based
If you know your exact conception date, this adds 266 days (38 weeks) — the average length of pregnancy from conception.
IVF Transfer Dating
The most precise method available, since the embryo's exact age is known at transfer — 261 days for a 5-day blastocyst, 263 days for a 3-day embryo.
Ultrasound Dating
Especially useful with an irregular cycle or uncertain LMP — measures fetal size to estimate gestational age directly.
Method Comparison
| Method | Days Added | Best For |
|---|---|---|
| LMP | 280 days | Regular cycles with a known period start date |
| Conception Date | 266 days | Known ovulation/conception date (e.g., fertility tracking) |
| IVF (5-Day Transfer) | 261 days | IVF pregnancies with blastocyst transfer |
| IVF (3-Day Transfer) | 263 days | IVF pregnancies with cleavage-stage transfer |
| Ultrasound | 280 - gestational age at scan | Irregular cycles or unknown LMP |
Important Limitations
- Only ~5% of babies arrive on their due date: All methods estimate a probable window, not an exact day.
- Early ultrasound is generally most accurate: Scans done in the first trimester tend to be more precise than later ones.
- Your provider's dating takes precedence: If your due date has already been confirmed clinically, use that date over any calculator estimate.
Key Takeaways
- Choose the most precise method available to you. IVF and ultrasound dating are generally more accurate than LMP-based estimates.
- Different methods can give slightly different dates. This is normal and expected, not a sign of error.
- A due date is a target, not a deadline. Full-term birth spans a 5-week window (37-42 weeks).
- Consult your provider. No due-date method is exact — only about 5% of babies arrive on their estimated date, and your doctor's ultrasound dating should always take precedence.