Due Date Calculator
Estimate your pregnancy due date and current gestational age from your last period, conception date, or IVF transfer date.
How to use the due date calculator
- 1
Pick the dating method you know: last period, conception date, or IVF transfer date.
- 2
Enter the date, plus your average cycle length (LMP method) or embryo age at transfer (IVF method).
- 3
Your estimated due date, current gestational age, and trimester milestones appear instantly — no button to click.
How your due date is calculated
From your last period (Naegele's Rule): add 280 days (40 weeks) to the first day of your last menstrual period. For a last period starting January 1, 2026, that gives an estimated due date of October 8, 2026. If your average cycle is longer or shorter than 28 days, the calculator shifts the estimate by the difference — a 32-day cycle (4 days longer) pushes both the start of gestation and the due date 4 days later, to October 12, 2026.
From your conception date: add 266 days (38 weeks) directly to the date you conceived or ovulated. A conception date of January 15, 2026 gives the same due date as the LMP example above, October 8, 2026 — because conception typically occurs about two weeks after the LMP in a standard cycle.
From an IVF transfer date: because the embryo already has a known age at transfer, the formula subtracts that age. For a day-5 (blastocyst) transfer, add 261 days to the transfer date; for a day-3 transfer, add 263 days. A transfer on January 20, 2026: a day-5 transfer gives a due date of October 8, 2026, while a day-3 transfer (2 days younger at transfer) gives October 10, 2026 — 2 days later.
Gestational age is simply how much time has passed since your LMP-equivalent start date. For a January 1, 2026 start, checking on April 10, 2026 gives 99 days elapsed, or 14 weeks, 1 day pregnant.
Pregnancy milestones explained
| Milestone | Gestational age |
|---|---|
| End of first trimester | 13 weeks |
| Second trimester begins | 14 weeks |
| Viability milestone | 24 weeks |
| Third trimester begins | 28 weeks |
| Early term begins | 37 weeks |
| Full term begins | 39 weeks |
| Due date | 40 weeks |
| Late term begins | 41 weeks |
Trimester and term boundaries follow common clinical convention (including ACOG's early/full/late-term definitions), but your own provider's terminology or dating may vary slightly.
Why due dates are estimates, not guarantees
An estimated due date is exactly that — an estimate built from population averages, not a prediction of the actual day of birth. Only around 1 in 20 babies are born on their exact estimated due date. Most full-term babies arrive somewhere in a window spanning roughly two weeks before to one week after it.
The LMP method assumes a textbook 28-day cycle with ovulation on day 14 — but real cycles vary, and even entering your own average cycle length is still an approximation of when ovulation actually happened that month. This is why an early ultrasound (typically between 8 and 13 weeks), which measures the size of the embryo or fetus directly, is generally considered more accurate than LMP dating alone and is often used to confirm or adjust the estimated due date.
Use this calculator to get a solid working estimate and to understand upcoming trimester milestones, but treat the exact date as a planning target rather than a fixed appointment — and always follow your doctor or midwife's official dating and prenatal care schedule.
Once your baby arrives, track their exact age in years, months, and days with our Age Calculator →
Frequently asked questions
Related guides
The three ways to calculate a pregnancy due date — last period, conception date, and IVF transfer — with the exact formulas and worked examples for each.
Read the guide →How gestational age is counted in weeks and days from your last period, why it starts before conception, and how to calculate it yourself.
Read the guide →How last-period dating and early ultrasound dating can produce different due dates, and why doctors often adjust to whichever is more reliable for your situation.
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