Pregnancy Calculator
Pregnancy Due Date Calculator works out Estimated due date and Day of the week from Dating method, First day of the last menstrual period and Average cycle length. The default figures on this page give estimated due date of 2026-10-08; change any entry and the result, the working and the sources update together.
Your figures
Updates as you typeHow this is worked out
5 steps
- Ovulation is one luteal phase before the next period would start: 28 - 14 = day 14 of the cycle, so 2026-01-15.
- Estimated due date = ovulation + 266 days.
- With a 28-day cycle this is exactly Naegele's rule: LMP + 280 days.
- Estimated due date = 2026-10-08 (Thursday).
- On 2026-06-01 the pregnancy is 151 days from the dating LMP, i.e. 21w 4d.
Dating milestonestable
| label | gestationalAge | date |
|---|---|---|
| End of first trimester | 13 6/7 weeks | 2026-04-08 |
| Start of second trimester | 14 0/7 weeks | 2026-04-09 |
| Anatomy scan window opens | 18 0/7 weeks | 2026-05-07 |
| Limit of periviability | 24 0/7 weeks | 2026-06-18 |
| Start of third trimester | 28 0/7 weeks | 2026-07-16 |
| Early term begins | 37 0/7 weeks | 2026-09-17 |
| Full term begins | 39 0/7 weeks | 2026-10-01 |
| Estimated due date | 40 0/7 weeks | 2026-10-08 |
| Late term begins | 41 0/7 weeks | 2026-10-15 |
| Postterm begins | 42 0/7 weeks | 2026-10-22 |
Its 5 worked examples are re-run on every release, last on 15 September 2026. What changed
Sources and references
3 sources
What the Pregnancy Due Date Calculator calculates
Estimates the due date from the last menstrual period, a known conception date, an ultrasound gestational age or an IVF embryo transfer, with gestational age, trimester and term milestones.
How to use this Pregnancy Due Date Calculator
Enter Dating method, First day of the last menstrual period, Average cycle length and Luteal phase length. Estimated due date updates as you type, and “Use a worked example” loads checked figures you can adjust. Change one figure at a time to see what drives the result.
How the result is worked out
Open “How this is worked out” beside the result for the step-by-step calculation behind Estimated due date, Day of the week and Dating LMP.
The method follows ACOG Committee Opinion No. 700: Methods for Estimating the Due Date, ACOG Committee Opinion No. 579: Definition of Term Pregnancy and Parikh MN et al., Prediction of the date of confinement in women with cycles other than 28 days.
Naegele's rule: LMP 1 January 2026, 28-day cycle example
With Dating method: lmp, First day of the last menstrual period: 2026-01-01, Average cycle length: 28, Show progress as of: 2026-06-01, the calculator returns Estimated due date: 2026-10-08, Estimated conception date: 2026-01-15, Gestational age in days: 151. This example is checked against an independent source in the test suite.
What you can compare
Change one input at a time to see how it affects Estimated due date, Day of the week and Dating LMP. The inputs you can vary are Dating method, First day of the last menstrual period, Average cycle length, Luteal phase length, Conception or ovulation date and Date of the ultrasound.
Understanding Estimated due date, Day of the week and Dating LMP
An estimate from calendar arithmetic, not a clinical assessment. Only about 4% of births occur on the estimated due date; ultrasound dating by a clinician supersedes menstrual dating when they disagree.
Results are general information, not financial, tax, legal, medical or engineering advice. Check any decision that matters with a qualified professional.
See something wrong? Report a problem with this calculator
Frequently asked questions
Is 4 weeks pregnant actually 2 weeks?
Estimates the due date from the last menstrual period, a known conception date, an ultrasound gestational age or an IVF embryo transfer, with gestational age, trimester and term milestones. Put your own figures in above and the working updates beside the result. For scale, the default figures on this page give 2026-10-08.
How do you calculator a pregnancy?
Estimates the due date from the last menstrual period, a known conception date, an ultrasound gestational age or an IVF embryo transfer, with gestational age, trimester and term milestones. Open “How this is worked out” beside the result to see each step for your own figures.
How accurate is a pregnancy due date calculator?
The Pregnancy Due Date Calculator follows the stated method, but the result is only as reliable as Dating method, First day of the last menstrual period, Average cycle length, Luteal phase length and Conception or ovulation date and the assumptions shown. Check the working and sources before relying on it for an important decision.
What information do I need for the Pregnancy Due Date Calculator?
You need Dating method, First day of the last menstrual period, Average cycle length, Luteal phase length, Conception or ovulation date, Date of the ultrasound, Gestational age at the scan (weeks) and Gestational age at the scan (extra days). The page opens with default figures that give estimated due date of 2026-10-08, so you can see the scale before entering your own.
What does this Pregnancy Due Date Calculator show?
It shows Estimated due date, Day of the week, Dating LMP, Estimated conception date, Dating method used, Gestational age today, Weeks pregnant and Extra days, with the working and any warnings for your entries.
Can I check how the Pregnancy Due Date Calculator result was calculated?
Yes. The “How this is worked out” section shows the calculation steps, and the sources section identifies the references used for the method.