Pregnancy Calendar Calculator
Use this tool to estimate your due date, conception date, current gestational age, and major pregnancy milestones.
Important: This calculator gives estimates only and does not replace care from your OB-GYN or midwife.
How this calendar pregnancy calculator works
A pregnancy calendar calculator estimates timing based on the first day of your last menstrual period (LMP). Most pregnancies are measured as 40 weeks (280 days) from LMP, not from conception. That means gestational age includes roughly two weeks before ovulation occurs.
This tool uses a standard obstetric method and adjusts for cycle length. If your cycle is longer than 28 days, ovulation often occurs later, which may shift your estimated due date. If your cycle is shorter, your estimate may shift earlier.
What your results mean
Estimated due date (EDD)
Your due date is an estimate of when you reach 40 weeks pregnant. Only a small percentage of babies are born exactly on this date. Most births happen in a normal window around it.
Estimated conception date
This is based on expected ovulation timing. For regular cycles, ovulation commonly occurs about 14 days before your next period. In a 28-day cycle, that is typically around day 14.
Gestational age
Gestational age is how far along pregnancy is on a specific date. It is expressed in weeks and days (for example, 21 weeks and 3 days). Clinicians use this measure for tests, scans, and monitoring growth.
Pregnancy calendar milestones (general guide)
- Week 4–5: Many people first get a positive home pregnancy test.
- Week 8: Early prenatal check-in is common.
- Week 11–13: First trimester screening window.
- Week 18–22: Anatomy ultrasound is often scheduled.
- Week 24–28: Gestational diabetes screening is common.
- Week 35–37: Group B strep screening is often done.
- Week 39+: Considered full term.
Tips for more accurate planning
Use the earliest reliable date
If you know your LMP clearly, start there. If cycles are irregular, an early ultrasound may provide a more accurate dating estimate than LMP alone.
Track cycle length honestly
Enter your true average cycle length from recent months. A better cycle estimate can improve your predicted conception and due date.
Update your timeline after medical visits
Your clinician may adjust your due date based on ultrasound measurements, especially in early pregnancy. Keep that medical estimate as your primary reference.
Frequently asked questions
Is this calculator exact?
No. It is a calendar estimate. Actual delivery date varies naturally.
Can I use it with irregular cycles?
Yes, but uncertainty is higher. If cycles vary a lot, use this as a rough guide and confirm dating with your healthcare provider.
Why does pregnancy count from LMP instead of conception?
It is the standard medical convention. LMP is usually easier to identify than exact conception day, so it supports consistent tracking across prenatal care.
Bottom line
A calendar pregnancy calculator is a practical planning tool for appointments, maternity timelines, and general expectations. Use it to stay organized, but always rely on clinical guidance for decisions about your pregnancy care.