Due Date Calculator — Estimate Your Due Date
What is Due Date Calculator — Estimate Your Due Date
A due date calculator estimates when your baby is likely to arrive, based on the first day of your last menstrual period (LMP). It uses Naegele's rule, which adds 280 days (40 weeks) to the first day of your last period. If your cycle is longer or shorter than 28 days, the estimate shifts by the difference. Keep in mind that only about 1 in 20 babies is born on the exact due date, and an early ultrasound dating scan is more accurate. This tool does not replace prenatal care.
How to use
- Enter the first day of your last menstrual period.
- Set your average cycle length in days (the default is 28).
- Read your estimated due date, shown in your local date format.
- See how many weeks and days along you are today, plus your trimester.
When to use it
Just found out you are expecting and want a date to plan around? Enter the first day of your last period and your cycle length. If your last period started on January 1 with a 28-day cycle, you get an estimated due date of October 8, roughly 40 weeks later, with conception estimated around January 15. The result updates live as you adjust the date, giving you a clear starting point to discuss with your midwife or doctor.
Frequently asked questions
How is my due date calculated?
This tool uses Naegele's rule: it adds 280 days (40 weeks) to the first day of your last menstrual period. If your cycle is not 28 days, the estimate is adjusted by the difference between your cycle length and 28 days.
How accurate is a due date calculator?
It gives a solid estimate, but only about 1 in 20 babies arrives on the exact due date. An early ultrasound dating scan is more accurate, especially if your cycle is irregular. Use this as a guide, not a guarantee.
What if my cycle isn't 28 days?
Enter your real average cycle length. A longer cycle pushes the due date later and a shorter cycle brings it earlier, because ovulation happens later or earlier than the standard day 14.
Can it work from a conception or IVF date?
This calculator uses the last menstrual period method, not a conception or embryo transfer date. If you know your conception date, you can approximate the last period as about two weeks before it, but for IVF a due date based on the transfer date is more reliable.
Can I share this tool with my dates already filled in?
Yes. The URL updates automatically as you enter your dates. Copy it from the address bar or use the Share button — anyone who opens the link will see your exact inputs ready to go.
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