Pregnancy Due Date Calculator
Example: LMP March 1 → Due date December 6 (40 weeks)
Calculate your estimated due date and see how far along you are in your pregnancy. Enter the first day of your last period or conception date to get your timeline and key milestones.
Calculation results updated
40-Week Pregnancy Timeline
Due Date
Estimated Gestational Age
Trimester
Days Remaining
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How We Calculate This
Estimated due date = LMP + 280 calendar days, or known conception date + 266 days. Gestational age counts calendar days from LMP to today; conception mode uses a dating origin 14 days before conception. That origin is an estimate, not a record of your actual period. Today follows your device's local date. The timeline uses ACOG trimester boundaries at 14 and 28 weeks. Milestones are estimated calendar landmarks; the usual anatomy scan window is 18–22 weeks, with individual timing set by your clinician.
Methodology last reviewed: September 2026. How SparkCalc works
Sources: ACOG Committee Opinion No. 700: Methods for Estimating the Due Date · ACOG: How Your Fetus Grows During Pregnancy · ACOG Committee Opinion No. 579: Definition of Term Pregnancy · ACOG: Ultrasound Exams
Frequently Asked Questions
How is the due date calculated?
The estimate adds 280 days (40 weeks) to the first day of your last menstrual period (LMP), or 266 days to a known conception date. LMP dating assumes a regular 28-day cycle with ovulation around day 14; this calculator does not adjust for other cycle lengths.
How accurate is the due date?
A due date estimates pregnancy timing, not the exact day of birth. First-trimester ultrasound is the most accurate way to establish or confirm gestational age. Irregular cycles, uncertain period dates and variable ovulation can make a calendar estimate less reliable.
What if I conceived via IVF?
Use the due date assigned by your fertility clinic. To reproduce the calendar estimate here, choose conception date and enter the transfer date minus the embryo age in days. A day-5 transfer gives a due date 261 days after transfer; a day-3 transfer gives 263 days.
When do the trimesters start?
Using ACOG definitions, the first trimester runs from the first day of your LMP through 13 weeks and 6 days. The second begins at 14 weeks, and the third at 28 weeks. Early term begins at 37 weeks; full term begins at 39 weeks.
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For educational use only. This calendar estimate cannot confirm pregnancy, assess fetal development or determine when delivery is safe. Use the due date and care schedule agreed with your healthcare professional, especially with irregular cycles, uncertain dates or assisted reproduction.