Pregnancy Due Date Calculator
Estimate your due date and track key pregnancy milestones
Calculation Method
Results
Enter your information and click Calculate
What is the Pregnancy Due Date Calculator?
A pregnancy due date calculator will provide you with an estimated date when your baby is likely to be born based on the first day of your last menstrual period (LMP) or your conception date. It’s one of the first things expectant parents want to know and one of the first things an OB or midwife will calculate at an initial appointment. CalciHub’s version provides your estimated due date, your current gestational age in weeks and days, and a detailed breakdown of all three trimesters, so you know exactly where you are in the pregnancy timeline.
How Does a Pregnancy Due Date Calculator Work?
The primary method is Naegele’s Rule, which is used by most health care providers worldwide.
Formula: Due date = LMP + 280 days (40 weeks)
Or in other words due date = LMP + 9 months + 7 days
LMP = the first day of your last menstrual period 280 days = the average length of a full-term pregnancy from LMP 40 weeks = same duration expressed in weeks
If you know your conception date instead, the calculator adds 266 days (38 weeks) from that date.
How to Use CalciHub's Pregnancy Due Date Calculator
1. Choose your input method: last menstrual period date or conception date.
2. Pick the date of interest from the date picker.
3. If you are using LMP, optionally enter your average cycle length (default 28 days).
4. Click Calculate.
5. View your estimated due date, current week of pregnancy, and trimester breakdown.
Tip: An ultrasound in the first trimester is still the most accurate way to confirm your due date, especially if your cycle is irregular. Use this calculator as a guide, then confirm with your provider.
A Quick Example
Lisa's last menstrual period started on March 1, 2025. She enters that date into CalciHub's pregnancy due date calculator.
LMP: March 1, 2025 | Cycle length: 28 days
Estimated due date: December 6, 2025 Current gestational age (as of late May): approximately 12 weeks and 3 days First trimester ends: around June 7, 2025
Lisa shares the due date with her family and brings the result to her first OB appointment. Her doctor confirms with an ultrasound that the dates line up closely. Knowing her trimester timeline helps her plan for maternity leave and prenatal appointments.
Frequently Asked Questions
The calculator gives an estimate based on average cycle length and pregnancy duration. Only about 5% of babies arrive exactly on their due date. A first-trimester ultrasound is more accurate, especially for women with irregular cycles.
Use your conception date if you know it, the calculator accepts that input too. If you know neither, an early ultrasound can date the pregnancy based on fetal measurements. Your healthcare provider can help establish the timeline.
Gestational age is counted from the first day of the last menstrual period, it's what doctors and this calculator use. Fetal age (also called embryonic age) counts from conception and is typically about two weeks less. Most pregnancy milestones use gestational age.
The first trimester runs from conception through week 12. The second trimester covers weeks 13 through 26. The third trimester goes from week 27 until birth. CalciHub's calculator shows all three trimesters with their dates based on your specific LMP.
Yes, completely free. No sign-up required, just enter your date and get your full pregnancy timeline instantly.
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