Pregnancy Due Date Calculator
Estimate your pregnancy due date, weeks and days, and trimester dates using your last period, known conception date or clinician-provided due date.
A clearer view of your dates
See your estimated due date, weeks and days, and trimester milestones.
Enter your details and select Calculate. No signup needed.
For general information only. This tool does not confirm pregnancy, diagnose fertility conditions or replace clinical care. Ultrasound dating and your clinician’s assessment may differ from this estimate.
How to use this pregnancy calculator
- Choose the date you know: your last period, a known conception date, or the due date your clinician gave you.
- Enter the date. For the period method, adjust your usual cycle length if needed.
- Select Calculate to see the estimate. Copy or print the summary if you want to discuss it at an appointment.
Changing an input clears the old result so you do not accidentally use an estimate based on different dates. Nothing is calculated until you submit the form.
How the due date is estimated
For the last-period method, the calculation adds 280 days to the first day of your last menstrual period, then adjusts by the difference between your cycle length and 28 days. This is a calendar approximation based on an assumed ovulation pattern.
Example: a last period starting January 1, 2026 with a 28-day cycle gives an estimated due date of October 8, 2026. With a 30-day cycle, the estimate moves to October 10.
The known-conception method adds 266 days. The date of intercourse does not necessarily establish conception. If you already have a clinician-provided due date, use that option; the tool will derive calendar milestones without trying to replace the clinical estimate.
Weeks and days, explained
Gestational age is counted from a dating origin approximately two weeks before conception, not from fertilization itself. Here, we derive that origin by subtracting 280 days from the due date, then count complete weeks and remaining days to today in your device’s local calendar. Cycle-adjusted results may therefore differ from simply counting days since your period.
The milestone list marks 14 and 28 weeks. These are calendar markers, not appointment recommendations.
When a calendar estimate may not fit
Irregular cycles, an uncertain period date and differences in ovulation timing can make this estimate less useful. Ultrasound and your clinician’s assessment may give a different date. IVF and other assisted-reproduction pregnancies require treatment-specific dating; use the due date your care team provides.
A due date is an estimate, not a promise about when birth will happen. This calculator does not confirm pregnancy or assess whether a pregnancy is progressing normally.
Common questions
Does this calculator confirm that I am pregnant?
No. It performs date arithmetic only. A pregnancy test and appropriate clinical care are needed to establish and assess a pregnancy.
Why is my scan due date different?
Calendar estimates rely on assumptions about your cycle. A dating scan provides other information. Discuss differences with your clinician rather than changing your clinical due date based on this website.
Can I save my estimate?
Use Copy summary or Print / Save PDF. Your entries are not automatically saved here. A copied or downloaded summary contains personal information, so choose where you store it.
Can I use this for an irregular cycle?
The period-based method is not reliable for irregular cycles. If you have one, select a due date provided by your clinician.
Sources and editorial transparency
Prepared by DateTimeWise. Calculation documentation updated September 24, 2026. This page has not been independently medically reviewed.
Have a calculation concern? Contact DateTimeWise with a fictional example rather than personal medical details.