Pregnancy Due Date Calculator
Estimate your due date from the first day of your last period.
All calculations happen locally in your browser — nothing is uploaded, stored or tracked.
Enter your last period date
The first day of your last menstrual period.
Set your cycle length
Defaults to 28 days; adjust if yours differs.
Read the estimate
Due date, conception date, weeks pregnant and trimester.
What Is a Pregnancy Due Date Calculator?
A due date calculator estimates when a baby is likely to be born. The standard method (Naegele's rule) adds 280 days — 40 weeks — to the first day of the last menstrual period (LMP). Only about 5% of babies arrive exactly on their due date; most are born within two weeks either side.
The calculator also estimates the conception date (roughly 14 days after the LMP for a typical 28-day cycle), the current gestational age in weeks and days, the trimester, and how many days remain.
The Estimate
If your cycle length differs from 28 days, adjust by adding (cycle length − 28) days. The calculator includes a cycle-length field for this.
Limitations
Your data never leaves your device.
Every calculation on this site runs in your browser using vanilla JavaScript. Nothing is uploaded, stored or tracked.
- 100% local, client-side calculations
- No data stored on any server
- No tracking, no analytics, no ads scripts
- Works offline once loaded
Frequently Asked Questions
How is my due date calculated?
Add 280 days (40 weeks) to the first day of your last menstrual period — Naegele's rule.
Why is my due date an estimate?
Conception timing and cycle length vary, so due dates are estimates. Only about 5% of births happen exactly on the due date.
How many weeks pregnant am I?
The calculator counts from the LMP. Most pregnancies last 40 weeks from that date.
What if my cycle is longer than 28 days?
Add (cycle length − 28) days to the due date. The calculator's cycle field does this automatically.
When does the second trimester start?
Conventionally at 14 weeks, and the third at 28 weeks. The calculator shows your current trimester.