Due Date Calculator
Due Date Calculator — calculate your due date from LMP, conception, or IVF transfer. Shows gestational age, trimester, and milestones. Free, no signup.
Pregnancy milestones
| Week | Date | Milestone |
|---|
About Due Date Calculator
The Due Date Calculator estimates your expected date of delivery (EDD) using the method you choose — last menstrual period, known conception date, or IVF transfer date. The result includes your current gestational age, trimester, days remaining, and a week-by-week milestone timeline.
How due date calculation works
The standard formula for LMP dating is Naegele’s rule: add 280 days to the first day of your last menstrual period. This assumes a 28-day cycle with ovulation on day 14. If your cycle is longer or shorter, the calculator adds or subtracts the difference — a 35-day cycle gives a due date 7 days later than the 28-day default.
For conception-based dating, 266 days are added (280 − 14, since conception occurs ~14 days into the cycle). For IVF, the calculation is based on embryo age at transfer: a Day 5 blastocyst adds 261 days; a Day 3 embryo adds 263 days.
Gestational age vs. fetal age
Gestational age is counted from LMP, not from conception. This means at the point of conception, you are already “2 weeks pregnant” by gestational counting. Ultrasound measurements track gestational age to maintain consistency with LMP-based dating used throughout clinical care.
Trimester breakdown
| Period | Weeks from LMP | Key events |
|---|---|---|
| First trimester | 1–12 | Organogenesis, NT scan, NIPT |
| Second trimester | 13–27 | Anatomy scan, fetal movement |
| Third trimester | 28–40+ | Lung maturation, GBS test, delivery |
When due dates change
The LMP estimate can shift after an ultrasound dating scan, particularly in the first trimester. If measurements differ by more than ~5–7 days from the LMP date, many clinicians revise the EDD to the ultrasound-based date. After 20 weeks, ultrasound dating becomes less precise and the EDD is rarely changed.
Key pregnancy milestones
The milestone timeline in this calculator covers weeks 6–42, including the NT scan (week 12), anatomy scan (week 20), viability milestone (week 24), full term (week 39), and the due date itself (week 40). Past milestones are shown dimmed; upcoming milestones are shown in full.
All calculations happen in your browser. No data is sent to TheToolBus. This calculator is an estimate — confirm your due date with your healthcare provider.
Frequently asked questions
The standard method is Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period. If your cycle is shorter or longer than 28 days, the calculator adjusts — for example, a 35-day cycle shifts the due date 7 days later.
LMP dating is accurate within ±2 weeks for most people with regular cycles. The earlier an ultrasound is done (ideally before 14 weeks), the more precise the estimate. Many clinicians confirm or revise the EDD after the first-trimester dating scan.
Conception-based dating adds 266 days (38 weeks) to the date of conception. This is equivalent to adding 280 days to an LMP 14 days before conception. If you tracked ovulation precisely, this method can be more accurate than LMP alone.
For a Day 5 blastocyst transfer, the due date is 261 days after the transfer date. For a Day 3 transfer, it is 263 days after. These figures account for the embryo's age at transfer relative to the equivalent post-LMP gestational age.