Estimate your pregnancy due date three ways — last menstrual period, conception date, or IVF transfer — plus weeks pregnant, trimester, and milestone dates.
Results update live as you change values.
Estimated due date
Conception
—
Current week
—
Trimester
—
Days until due
—
| Stage | Weeks | Date | Status |
|---|
The Formula
For the LMP method we use Naegele's rule: add 280 days (40 weeks) to the first day of your last period, then adjust for cycle length. For conception, we add 266 days. For IVF, we subtract the embryo age (3 or 5 days) plus 14 days to reach a virtual LMP, then add 280.
All three converge on the same underlying truth: gestation is ~280 days from LMP. The choice of method depends on what information you have.
Three Methods
About This Tool
A due date calculator estimates when your baby is most likely to arrive — typically 40 weeks (280 days) from the first day of your last menstrual period. It's the same arithmetic clinicians use, with adjustments for cycle length and for pregnancies conceived via IVF.
The LMP method (Naegele's rule, 1830s) is the most common because LMP is easy to remember. The conception method is more precise if you know your ovulation/conception day. The IVF method is the most accurate of all, because the transfer day is known exactly and embryo age is documented.
Worth knowing: only about 5% of babies arrive on their exact due date. Most arrive within two weeks either side. A first-trimester ultrasound (8–12 weeks) is the gold-standard dating method, accurate to within ±5 days.
Three Methods
LMP, conception, or IVF transfer — use what you know.
Live Weekly Progress
See exactly where you are in the 40-week journey.
Trimester Timeline
Start and end dates for each trimester, mapped out.
Cycle-Length Aware
Adjusts when your cycle isn't a standard 28 days.
IVF-Ready
Supports both 3-day and 5-day blastocyst transfers.
100% Free & Private
No account needed. All maths runs in your browser.
Three methods, one estimate — pick whichever fits what you know.
LMP is the default and easiest. Use Conception if you know your ovulation day. Use IVF for transferred embryos.
For LMP, use the first day of your last period — not the last day.
Default is 28 days. Shorter or longer cycles shift ovulation — and therefore your due date.
3-day embryos and 5-day blastocysts subtract different amounts from the transfer date.
The big number is your estimated due date. Stats show conception date, current week, and trimester.
A first-trimester ultrasound is the most accurate dating tool — use this as a starting estimate.
Everything you need to know about pregnancy dating.
For LMP, Naegele's rule adds 280 days (40 weeks) to the first day of your last menstrual period. Conception adds 266 days. IVF transfer subtracts the embryo age (3 or 5 days) and counts back to a virtual LMP.
About 5% of babies arrive on their exact due date. Most arrive within 2 weeks either side. A first-trimester ultrasound (8–12 weeks) is the most accurate dating method, accurate to ±5 days.
For known cycles, LMP works well. For IVF, the transfer date is the most precise because conception timing is known to the day. Conception date is accurate if you tracked ovulation; otherwise it's just LMP + 14.
Cycle length matters because ovulation timing shifts. A 35-day cycle moves ovulation to ~day 21 instead of day 14 — and the due date by a week. This calculator adjusts automatically when you change cycle length.
1st trimester: weeks 1–12. 2nd trimester: weeks 13–26. 3rd trimester: weeks 27–40+. Most prenatal scans, screenings, and major fetal milestones map to these windows.
Use the conception method if you tracked ovulation, or get an early ultrasound — the gold standard when LMP is uncertain. For IVF, the transfer date is always available in your clinic notes.
ACOG defines early term as 37–38 weeks, full term as 39–40 weeks, late term as 41 weeks, and post-term as 42+ weeks. Babies born at 37+ weeks generally have minimal complications related to prematurity.