The moment you confirm a pregnancy, the first thing you want to know is when you will get to meet your baby. The Due Date Calculator estimates your delivery date from just the first day of your last menstrual period (LMP) and tells you how many weeks and days pregnant you are today, along with whether you are in the first, second, or third trimester. It gives you the key dates at a glance — handy for scheduling prenatal visits, preparing baby supplies in advance, or looking up week-by-week development information.
The calculation follows Naegele's rule, the standard method used in obstetrics. It treats pregnancy as 280 days (40 weeks) from the first day of your last period and derives the due date from that. When your cycle is longer or shorter than 28 days, ovulation shifts later or earlier accordingly, so the due date is adjusted by the cycle difference for a more accurate estimate. Keep in mind that this is only a statistical estimate — the actual birth date can vary within roughly two weeks before or after the due date. Because the menstrual date you enter is sensitive information, it is never sent to a server and is calculated only inside your browser.
How to Use
- 1
Pick the first day of your last period
Use the date picker to select the first day your most recent period started — the day it began, not the day it ended.
- 2
Enter your average cycle length
Enter your average menstrual cycle length. If you are not sure, leave the standard value of 28 days as it is.
- 3
Check the result
Your estimated delivery date is shown along with your current pregnancy week, trimester, and the number of days remaining until the due date.
- 4
Copy the result
Use the copy button to save the due date and week information so you can use it to manage your appointment schedule.
When It's Useful
Schedule prenatal visits
Plan your routine checkups and key screenings in advance based on your due date and current pregnancy week.
Look up week-by-week information
Knowing exactly how many weeks and days along you are lets you find accurate fetal-development and maternal-change information for that week.
Plan baby supplies and leave
Seeing how many days remain until the due date helps you arrange baby supplies and time your maternity leave.
Identify your stage of pregnancy
Check which trimester you are in — first, second, or third — so you can keep track of the precautions for each stage.
Tips
- Pregnancy weeks are counted from the first day of your last period as week 0, day 0 — not from conception. Conception usually happens around the second week of pregnancy.
- If your cycle is irregular or your last period date is uncertain, a due date measured by ultrasound is more accurate. Treat this calculator's result as a reference only.
- Pregnancy is generally divided into the first trimester (weeks 1-13), second trimester (weeks 14-27), and third trimester (week 28 onward). Each stage has different precautions and screenings.
- The due date is a reference point, not the exact day of birth. Full term is considered weeks 37-42, and birth within that range is normal.
- Enter the first day your last period started, not the day it ended, for an accurate result. If you are unsure, check the date you noted down.
- If your cycle differs from 28 days, this calculator adjusts the due date by that difference. The longer the cycle, the later the due date is pushed.
FAQ
How is the due date calculated?
It follows Naegele's rule, adding 280 days (40 weeks) to the first day of your last period. If your cycle differs from 28 days, it adjusts by that difference.
What if I do not know my cycle length?
Use the default of 28 days. Most people fall between 25 and 35 days, and 28 days is the most common average value.
How does a cycle other than 28 days change the due date?
A longer cycle means later ovulation, so the due date is pushed back accordingly. For example, with a 32-day cycle, 4 days are added to the standard 280 days.
Are pregnancy weeks counted from the day of conception?
No. Medically, pregnancy weeks are counted from the first day of your last period as week 0. That is why the count is about two weeks ahead of actual conception.
How are the trimesters divided?
This calculator shows under 14 weeks as the first trimester, weeks 14-27 as the second trimester, and 28 weeks or more as the third trimester.
Will I definitely give birth on the calculated due date?
Only about 5% of births happen exactly on the due date. Most occur within two weeks before or after, and birth between weeks 37 and 42 is considered normal.
Is the menstrual date I enter saved?
No. Your period date and cycle are used only for calculation inside your browser; nothing is sent to a server or stored.