Due Date Calculator
Calculate your due date using one of four methods: last menstrual period (LMP), conception date, IVF transfer, or ultrasound. This is a support page — the head term "due date calculator" is locked by institutions, so we do not target it for organic search.
Calculate Your Due Date
The Four Methods
1. Last Menstrual Period (LMP)
EDD = LMP + 280 + (cycle length − 28)
This is the standard method (Naegele's rule with cycle correction). It assumes ovulation occurs 14 days before the next expected period.
2. Conception Date
EDD = Conception date + 266 days
This is more accurate than LMP if you know the conception date (for example, from IVF or known intercourse).
3. IVF Transfer
EDD = Transfer date + 263 days (Day 3) or + 261 days (Day 5)
IVF dating is the most precise method because the exact date of fertilization is known.
4. Ultrasound Dating
EDD = Ultrasound date + (280 − gestational age at ultrasound in days)
First-trimester ultrasound is the most accurate dating method. ACOG recommends using the ultrasound date if it differs from the LMP date by more than 7 days.
Which Method Is Most Accurate?
| Method | Accuracy | Notes |
|---|---|---|
| IVF transfer | Most accurate | Exact fertilization date known |
| First-trimester ultrasound | ± 5 days | CRL measurement |
| Conception date | ± 3-5 days | If known precisely |
| LMP with cycle correction | ± 7 days | Standard method |
| Second-trimester ultrasound | ± 8-14 days | Less accurate than first trimester |
| Third-trimester ultrasound | ± 21-28 days | Too unreliable to redate |
Source: ACOG Committee Opinion 700, Methods for Estimating the Due Date.
What If the Methods Disagree?
If your LMP-based due date and your ultrasound-based due date differ by more than 7 days, ACOG recommends using the ultrasound date. This is because ultrasound dating in the first trimester is more accurate than LMP-based dating.
When to Talk to Your Clinician
Contact your healthcare provider if:
- You are unsure which method to use
- Your due dates from different methods disagree
- You have irregular cycles
- You have questions about your due date
Related Tools
- Gestational Age Calculator — full results with gestational age
- How Many Weeks Pregnant — conversational framing
- Trimester Calculator — which trimester are you in?
- Pregnancy Milestone Dates — dated list of key milestones