Pregnancy due date calculator with LMP, conception and IVF methods
Select the dating event and enter its date. HitEquals estimates the due date, days remaining, gestational age on a reference date and key week boundaries. Use the date adopted by your clinician for care decisions.
Inputs used by this calculator
Pregnancy Calculator uses the fields below. The starting values reproduce the page example; replace them with values from the same units and time period before using the result.
| Input | Starting example | Accepted value | How it is used |
|---|---|---|---|
| Dating method | First day of last menstrual period (LMP) | First day of last menstrual period (LMP) · Known conception date · IVF day-3 embryo transfer · IVF day-5 embryo transfer | Chooses which Pregnancy Calculator method or unknown the engine evaluates. |
| LMP, conception or transfer date | 2026-09-01 | Text in the format shown | Supplies the lmp, conception or transfer date quantity used by the published equation or result breakdown. |
| Calculate timeline on | 2026-09-10 | Text in the format shown | Supplies the calculate timeline on quantity used by the published equation or result breakdown. |
How pregnancy dating works
Obstetric gestational age conventionally begins on the first day of the last menstrual period, about two weeks before conception in a regular 28-day cycle. That makes the standard LMP interval 280 days, or 40 weeks.
Due date formulas
A known conception date uses 266 days. ACOG gives specific assisted-reproduction offsets: add 263 days to a day-3 embryo transfer or 261 days to a day-5 transfer.
EDD=LMP+280 daysEDD=conception+266 daysEDD=day-3 transfer+263 daysEDD=day-5 transfer+261 daysWorked LMP example
Starting from September 1, 2026 and adding 280 days gives June 8, 2027. On September 10, the calculated gestational age is 1 week and 2 days and 271 days remain.
Ultrasound and the documented due date
ACOG describes first-trimester ultrasound as the most accurate way to establish or confirm gestational age. Once a clinician selects the best obstetric estimate, changes should be uncommon and documented.
Why LMP dating can differ
The 280-day rule assumes a 28-day cycle with ovulation on day 14. Recall error, cycle length variation, irregular ovulation and recent hormonal contraception can shift the relationship between LMP and conception.
Reading weeks and trimesters
The result reports completed weeks plus remaining days. Milestone dates are calendar estimates based on the selected due date. Clinical definitions and care schedules may use more precise week-and-day boundaries.
Dating method offsets
| Input event | Days to estimated due date |
|---|---|
| LMP | 280 |
| Known conception | 266 |
| IVF day-3 transfer | 263 |
| IVF day-5 transfer | 261 |
Frequently asked questions
Is the due date exact?
No. It is an estimate used to organize gestational age and care.
Why does LMP use 40 weeks?
The convention begins on the first day of the last menstrual period, typically before conception.
Which dating method is most accurate?
ACOG says first-trimester ultrasound is the most accurate method to establish or confirm gestational age.
How is an IVF due date calculated?
ACOG uses the embryo age and transfer date: 263 days after a day-3 transfer or 261 after a day-5 transfer.
What if my cycle is not 28 days?
The standard LMP assumption may fit less well; discuss the best obstetric estimate with your clinician.
Should I change my due date from this result?
Use the due date documented by your obstetric care professional.
What to keep in mind
A due date is an estimate. ACOG states that first-trimester ultrasound is the most accurate method to establish or confirm gestational age; clinicians document and revise dating under defined criteria.
Results are rounded for display in US format, with money in dollars and cents; CSV exports keep full calculation precision. This is a calculation summary, not an official certificate.