Due Date Calculator
Free due date calculator and pregnancy due date calculator for educational dating. Start from LMP (default) or known conception/ovulation to view an estimated due date, gestational age, and trimester.
Pregnancy calculators and fetal growth reference tools for educational use.
Plain-language interpretation
An estimated due date (EDD) is a reference point near 40 weeks of gestational age, not a guarantee of delivery day. Most births occur in a window around the EDD. LMP-based dating assumes a roughly 28-day cycle with ovulation near day 14—your cycle may differ.
Formula and dating standard
- LMP method: first day of LMP + 280 days
- Known conception/ovulation: date + 266 days
- Estimated conception from EDD: EDD − 266 days
- IVF / embryo transfer: use the IVF due date calculator
Important assumptions
- LMP methods assume about 28-day cycles and mid-cycle ovulation.
- Actual conception day usually cannot be known exactly.
- ART pregnancies should prioritize embryo age and transfer date.
- Formal obstetric EDD should combine early ultrasound and clinical records.
Applicable use
Suitable for educational dating of ongoing pregnancies when LMP, or conception/ovulation timing is known. Not for diagnosing pregnancy, viability, or complications.
Worked example
LMP 2024-01-01 → EDD 2024-10-07 (280 days later). On assessment date 2024-04-01, gestational age is 91 days (13 weeks, 0 days), still in the first trimester under this site’s educational cutoffs.
Limitations
- Not a diagnosis or care plan.
- Irregular cycles make LMP dating less reliable.
- Does not replace early ultrasound dating when available.
- Does not manage twin pregnancies or specialized obstetric protocols.
References
- ACOG Committee Opinion — Methods for Estimating the Due Date
- Standard educational offsets: LMP + 280 days; conception + 266 days (not an official ACOG product page).
Frequently asked questions
- How does this pregnancy due date calculator work?
- By default it adds 280 days to the first day of the last menstrual period (LMP). If you know conception or ovulation timing, it adds 266 days instead.
- Is this an official ACOG calculator?
- No. Dating rules align with widely used ACOG pregnancy-dating conventions, but this site is independent and not an official ACOG tool or medical provider.
- Should IVF pregnancies use this page?
- Prefer the dedicated IVF due date calculator, which uses embryo age and transfer date rather than ordinary LMP rules.
- Can my clinical due date differ from this estimate?
- Yes. Formal obstetric EDD often integrates early ultrasound and clinical records, which may adjust or replace LMP-based estimates.
Last content review: 2026-07-18. Formula version: pregnancy-dates-v1.