Pregnancy Due Date Calculator
Estimate your due date from your last period or conception date, plus current week, trimester and key milestone dates.
Quick answer: Enter the first day of your last menstrual period (or a known conception date) and we estimate your due date — LMP + 280 days by Naegele's rule — along with your current week, trimester and milestone dates.
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Frequently asked questions
- How is the due date calculated?
- With Naegele's rule: your last period's first day plus 280 days (40 weeks). This assumes a 28-day cycle with ovulation around day 14; we let you adjust for longer or shorter cycles.
- How accurate is an estimated due date?
- It's an estimate — only about 4% of babies arrive on the exact date. Most births happen within two weeks either side. An early ultrasound dating scan is more accurate than LMP, especially with irregular cycles.
- What if my cycle isn't 28 days?
- Longer cycles usually mean later ovulation, pushing the due date back; shorter cycles pull it forward. Our cycle-length adjustment shifts the estimate by the difference from 28 days.
- Can I calculate from the conception date instead?
- Yes — switch to conception mode and we add 266 days (38 weeks), since conception is about two weeks after the LMP in a typical cycle.
- What are the milestone dates?
- We flag the end of the first trimester (~12 weeks), the anatomy-scan window (~20 weeks), the start of the third trimester (~28 weeks) and full term (~37 weeks) so you can see the timeline at a glance.
- How are pregnancy weeks counted?
- Gestational age is counted from the first day of your last period, not from conception — so at conception you're already considered 'two weeks pregnant'. That's the standard clinical convention.
- When do the trimesters start and end?
- Roughly: first trimester weeks 1–13, second trimester weeks 14–27, third trimester weeks 28 to birth. Exact boundaries vary slightly between sources.
- Is my information uploaded?
- No — all the date math runs in your browser. Your dates never leave your device.
- Is this a substitute for medical advice?
- No — it's an informational estimate. Your midwife or doctor will confirm dating with an ultrasound and monitor your pregnancy; always follow their guidance.
- Can I use it after an IVF transfer?
- Use conception mode and enter the transfer-adjusted date your clinic gives you (they account for embryo age). For precise IVF dating, follow the date your clinic provides.