Terminus Calculator — Deadline & Date Planner

Free terminus calculator. Calculate terminus dates and deadlines for legal, academic, and business purposes. Add or subtract days from any date easily.

Calculate Due Date

How to Use

Choose your method — last menstrual period (LMP) or known conception date.

Enter the date and your average cycle length (if using LMP). Default is 28 days.

Click Calculate to see your due date, current week, trimester, progress, and milestones.

What is a Due Date Calculator?

A due date calculator (also called a pregnancy calculator or terminus calculator) estimates when your baby will be born based on your last menstrual period or conception date. It uses Naegele's rule, which adds 280 days to the first day of your LMP. The calculator also shows your current week of pregnancy, which trimester you're in, a progress bar, and key developmental milestones. This is an estimate — consult your healthcare provider for an accurate due date.

Frequently Asked Questions

How is the due date calculated?
Using Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). If using conception date, 266 days (38 weeks) are added instead.
How accurate is the due date?
Only about 5% of babies are born on their exact due date. Most are born within 2 weeks before or after. The due date is an estimate, not a guarantee.
What is the difference between LMP and conception date?
LMP is the first day of your last period — the most commonly used method. Conception date is the actual date of fertilization, typically about 2 weeks after LMP.
What are the trimesters?
First trimester: weeks 1-12. Second trimester: weeks 13-27. Third trimester: weeks 28-40. Each stage has different developmental milestones.
Is this medical advice?
No. This calculator provides estimates for informational purposes only. Always consult your doctor or midwife for accurate pregnancy dating, especially after an ultrasound.

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