Due Date Calculator - Estimate your pregnancy due date
Optional: 28 days by default. The dates shift by as many days as your cycle differs from 28.
This is an estimate; only your doctor or midwife can confirm the dates, notably with the dating ultrasound.
How to use this calculator?
1. Choose whether you know the first day of your last period or the conception date.
2. Enter that date.
3. If you start from your last period, enter your average cycle length (28 days by default).
4. Read your estimated due date, how far along you are and the key dates.
Quick answer
How do you calculate your due date?
Add 280 days (40 weeks) to the first day of your last menstrual period, assuming a 28-day cycle; if your cycle is longer or shorter, shift the date by the same number of days. From the conception date, add 266 days. Example: a last period starting on 1 January 2026 gives an estimated due date of 8 October 2026.
| First day of last period | Estimated due date |
|---|---|
| 1 January 2026 | 8 October 2026 |
| 15 March 2026 | 20 December 2026 |
| 1 June 2026 | 8 March 2027 |
| 10 September 2026 | 17 June 2027 |
About the Due Date Calculator
What is it?
This calculator estimates your due date from the first day of your last menstrual period or from your conception date. It also shows how many weeks and days pregnant you are today, your current trimester and a few key dates.
Why use it?
Knowing your approximate due date helps you plan prenatal appointments, preparations and parental leave. It is only an estimate: the dating ultrasound performed early in pregnancy is what doctors and midwives use to confirm it.
How does it work?
Pregnancy is usually counted from the first day of the last period (Naegele's rule): due date = last period + 280 days (40 weeks), for a 28-day cycle. With a longer or shorter cycle, the date shifts by (cycle length - 28) days. From a conception date: due date = conception + 266 days.
Usage tips
- Use the first day of your last period, not the last day: it is the starting point of the calculation.
- Pregnancy weeks include the roughly two weeks before conception, which is why you are already "2 weeks pregnant" at conception.
- If your cycles are irregular, the estimate is less reliable: the dating ultrasound will refine it.
- In this tool the 1st trimester ends at week 14 and the 2nd at week 28, as a guide.
- Share the calculation link with your partner or family so everyone has the same dates.
Embed this tool on your website
Copy this code into your website or blog: the tool shows up right on your page, free and without sign-up.