Due Date Calculator
Estimated delivery date and pregnancy milestones.
Enter your values
Enter the first day of last period in YYYY-MM-DD.
Enter the cycle length in days.
Enter the today's date in YYYY-MM-DD.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Estimated due date
- 2026-12-06 (Sunday)
- Gestational age today
- 21 weeks, 2 days
- Trimester
- Second
- Conception (approx)
- 2026-03-15
- Days remaining
- 131
Quick answer
Naegele's rule estimates the due date as 280 days from the first day of the last menstrual period.
Due date = LMP + 280 days
At a glance
| What it does | Estimated delivery date and pregnancy milestones. |
|---|---|
| Category | Health |
| Inputs needed | First day of last period, Cycle length, Today's date |
| Main output | Estimated due date |
| Formula | Due date = LMP + 280 days |
| Cost | Free — no sign-up, no download |
How to use the Due Date Calculator
- 1Enter the first day of your last period.
- 2Adjust your average cycle length.
- 3Read the due date and current gestational age.
Inputs explained
- First day of last period(YYYY-MM-DD)
- Enter the first day of last period in YYYY-MM-DD.
- Cycle length(days)
- Enter the cycle length in days.
- Today's date(YYYY-MM-DD)
- Enter the today's date in YYYY-MM-DD.
Worked example
Using the values the calculator loads with:
Inputs
- First day of last period2026-03-01 YYYY-MM-DD
- Cycle length28 days
- Today's date2026-07-28 YYYY-MM-DD
Results
- Estimated due date2026-12-06 (Sunday)
- Gestational age today21 weeks, 2 days
- TrimesterSecond
- Conception (approx)2026-03-15
- Days remaining131
Frequently asked questions
How accurate is the due date?
Only about 4% of babies arrive on the estimated date; roughly 80% arrive within two weeks either side.
Why count from the last period?
Ovulation is hard to pin down, but the last period is a date most people know, so obstetrics standardised on it.
What do I need to enter into the Due Date Calculator?
Just 3 values: first day of last period, cycle length, today's date. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Due Date Calculator work out the answer?
Naegele's rule estimates the due date as 280 days from the first day of the last menstrual period. It applies the formula Due date = LMP + 280 days and shows the working so you can check each step by hand.
Is the Due Date Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.