Pregnancy Calculator
Adjust the inputs below. Results update as you type.
How it works
Gestational age is counted from the first day of the last menstrual period (LMP), not conception—so 'two weeks pregnant' typically predates fertilization. First trimester: weeks 1–13. Second: 14–26. Third: 27–40. Anatomy ultrasound at 18–20 weeks screens for structural anomalies. GBS screening at 36 weeks. Full term is 39–40 weeks; early term 37–38 weeks.
Input guidance
- Use measured values (recent weight, height, activity level) rather than guesses.
- Recalculate every few weeks as your routine and body metrics change.
- Pair screening metrics with context such as sleep, stress, and medical history.
The formula
Pregnancy is dated from the last menstrual period (LMP). Due date ≈ LMP + 280 days (40 weeks). Current gestational age = days since LMP, expressed in weeks and days.
Worked example
If the LMP was January 1, the estimated due date is about October 8 (280 days later), and 12 weeks of pregnancy would fall around late March.
More examples to test
- Maintenance case: keep activity constant and observe expected baseline ranges.
- Adjustment case: change only one major variable to understand sensitivity.
How to interpret results
Use results for awareness and planning, then validate with qualified medical or nutrition professionals for individualized decisions.
When this can be inaccurate
Population formulas cannot account for all biological factors such as medical conditions, medication effects, body composition differences, and genetics.
Change history
- July 2026: Quality-reviewed for publication with formula checks and explanatory copy updates.
Site-wide corrections also appear on the corrections log.
Track fitness goals with a top app
General wellness resource.
Frequently asked questions
How is pregnancy dated?+
Conventionally from the first day of the last menstrual period, so gestational age is about two weeks more than the time since conception.
How accurate is the due date?+
It is an estimate; only about 1 in 20 babies arrive on the exact date. Most births occur within two weeks either side of it.
What are the trimesters?+
First: weeks 1–12. Second: weeks 13–27. Third: weeks 28–40. Each brings different developmental milestones.
Can this calculator diagnose a condition?+
No. It is a screening and education tool only, not a clinical diagnosis.
When should I seek professional advice?+
Seek professional advice when results are extreme, persistent, or conflict with symptoms, goals, or prior medical guidance.