Maternity & Due Date Calculator
Use your last menstrual period (LMP) to estimate due date, current pregnancy week, trimester, and a maternity leave timeline.
This tool provides estimates only and does not replace medical advice from your OB-GYN or midwife.
How this maternity calculator works
Most due date tools use a standard pregnancy length of 280 days (40 weeks) from the first day of your last menstrual period. This is often called Naegele’s rule. Since cycle lengths vary, this calculator adjusts the estimate by adding or subtracting days from the standard 28-day cycle.
You also get a practical maternity planning view: your estimated conception date, current gestational age, trimester, and a suggested leave window based on your preferred start and leave duration.
What your results mean
Estimated due date
This is your projected delivery date based on LMP and cycle length. Only a small percentage of babies are born exactly on their due date, so think of this as a target point within a range.
Gestational age
Pregnancy weeks are counted from LMP, not from conception. So you may be considered “2 weeks pregnant” before ovulation even occurs. That’s normal in obstetric dating.
Trimester
- First trimester: Weeks 1–13
- Second trimester: Weeks 14–27
- Third trimester: Week 28 to birth
Planning maternity leave with confidence
A due date estimate helps with logistics: discussing handoff plans at work, organizing childcare for older children, and preparing medical, household, and financial plans before labor starts.
- Choose an intended leave start date (for example, 2 weeks before due date).
- Set a leave duration that matches your policy, benefits, and personal preferences.
- Use the timeline as a planning framework, then refine with your HR team and clinician.
Important notes and limitations
- Irregular cycles can reduce date accuracy.
- Early ultrasound measurements may shift your official due date.
- Fertility treatments or known ovulation dates may provide different dating methods.
- Always confirm key milestones with your prenatal care provider.
Frequently asked questions
Is this a medical diagnosis tool?
No. It’s an educational planning calculator. Your provider’s assessment is the clinical standard.
Can I use this if my cycle is not 28 days?
Yes. Enter your average cycle length. The due date estimate is adjusted by the difference from a 28-day cycle.
What if I am already past the due date?
The calculator will show how many days overdue the estimate is. Contact your provider for the right monitoring and next-step guidance.