Due Date Calculator
Estimate only; check important health decisions with a qualified professional.
2% – 55% reference display (not a diagnosis)
Estimate only; check important health decisions with a qualified professional.
Common questions
How is a due date calculated from the last menstrual period?
For a 28-day cycle, the standard calendar estimate is 280 days from the first day of LMP. This calculator also offers an approximate cycle-length adjustment.
How does a 35-day cycle affect the due date?
The simple cycle adjustment adds seven days compared with the 28-day estimate. Ovulation timing may differ in practice.
Can I calculate a due date from a conception date?
Yes. Select the Conception Date method and enter the date. The estimated due date is approximately 266 days later.
Is a due date the exact day my baby will be born?
No. Birth can occur before or after the assigned estimated due date. A calendar estimate is not a prediction of the actual delivery day.
What if my periods are irregular?
Cycle-based estimates may be less reliable when ovulation timing is unpredictable. Ask your prenatal clinician about appropriate pregnancy dating.
Can I enter ultrasound weeks and days here?
No. This version uses either LMP/cycle length or a conception date. Ultrasound dating should be interpreted with your healthcare team.
Does this tool calculate IVF transfer dates?
No. For IVF or frozen embryo transfers, use the estimated due date established by your fertility clinic using the embryo age and transfer date.
Which due date should I use when dates differ?
Use the estimated due date documented by your maternity or fertility team, especially when it is supported by early ultrasound or assisted reproduction records.
Related calculators
Learn more
Pregnancy Due Date by Last Period
Pregnancy due dates are commonly counted from the first day of the last menstrual period (LMP). In a conventional 28-day cycle, the estimated due date (EDD) is LMP + 280 days. With the cycle-length option, this calculator adds the difference between the entered cycle length and 28 days.
Example: LMP on 1 January 2026 gives an estimated due date of 8 October 2026 for a 28-day cycle. Entering a 35-day cycle shifts the estimate to 15 October 2026. The adjustment is a rough calendar assumption, particularly uncertain with irregular periods.
Due Date From a Conception Date
When a known or estimated conception date is selected, this calculator adds approximately 266 days (38 weeks). Conception can be uncertain even when the date of intercourse is known, so this method does not establish the date of fertilization or parentage.
Example: Conception estimated on 15 January 2026 gives a calendar due-date estimate of 8 October 2026. Medical dating may differ.
How Accurate Is an Estimated Due Date?
A due date is a clinical estimate, not a promise that delivery will occur on that date. First-trimester ultrasound can help establish or confirm pregnancy dating. Pregnancies following IVF require embryo-transfer-specific dating using documented clinical records; this page does not have an IVF or ultrasound input mode.
The Pregnancy Calculator specializes in gestational weeks and trimesters, while the Conception Date Calculator focuses on estimating possible fertilization timing from LMP. These are separate uses rather than duplicate due-date calculators.
Medical reference: ACOG — Methods for Estimating the Due Date. Follow the estimated due date established by your maternity care team.