How to use the Pregnancy Calculator
The pregnancy calculator estimates your due date and current week from the first day of your last period.
Open the Pregnancy Calculator →
What you need to enter
- First day of last period
- Cycle length (days)
The formula
Due date = last period + 280 days, adjusted for cycle length (+ cycle − 28).
Worked example
Using the default values in the calculator:
- First day of last period: 2026-10-13
- Cycle length (days): 28
| Estimated due date | Tue, 20 Jul 2027 |
| Today | 0 weeks 0 days |
| Trimester 2 starts | Tue, 19 Jan 2027 |
| Trimester 3 starts | Tue, 27 Apr 2027 |
Tips for better results
- Dating scans can change the date.
- Only about 5% of babies arrive on the due date.
Common mistakes to avoid
- Treating the date as exact.
- Using an irregular cycle without adjusting.
Please note: Health calculators and guides give general estimates, not medical advice. Talk to a doctor or other qualified professional about your own health. See our Disclaimer.