Last period, 28-day cycle
- Input
- First day of last period = 15 Sep 2026, Cycle = 28 days
- Working
- Due date = 15 Sep 2026 + 280 days = 22 Jun 2027. First trimester ends 21 Dec 2026; second trimester ends 29 Mar 2027.
- Result
- Due date = 22 Jun 2027
Pregnancy Due-Date Calculator
Calculate an estimated due date from last period, conception date or an ultrasound scan using Naegele's rule, with trimester milestone dates listed. Runs entirely in your browser — your numbers never leave this device.
Date from
Estimated due date
22 June 2027
- Gestational age today
- 6 weeks 5 days
- Days until due date
- 233
- First trimester ends
- 21 December 2026
- Second trimester ends
- 29 March 2027
| Milestone | Date |
|---|---|
| First trimester ends (13w6d) | 21 December 2026 |
| Second trimester ends (27w6d) | 29 March 2027 |
| Due date (40w0d) | 22 June 2027 |
These dates are calendar estimates calculated from Naegele's rule and the dates entered. An ultrasound measurement can give a different estimate.
Informational only. This calculator applies a published formula to the numbers you enter — it is not medical advice, a diagnosis, or a substitute for a clinician. Talk to a qualified professional about decisions concerning your health.
How it works
Naegele's rule: due date = first day of last period + 280 days, adjusted by (cycle length − 28) days | From conception: due date = conception date + 266 days | From ultrasound: due date = scan date + (280 − gestational age at scan in days)
| Trimester | Weeks |
|---|---|
| First trimester | Weeks 1–13 (to 13w6d) |
| Second trimester | Weeks 14–27 (to 27w6d) |
| Third trimester | Week 28 to birth |
Naegele's rule is the standard dating convention: a pregnancy is counted as 280 days — 40 weeks — from the first day of the last menstrual period, for a 28-day cycle. Longer or shorter cycles adjust the count day for day: a 32-day cycle adds four days, giving 284. The same 280-day span can be counted from other starting points: conception is dated 14 days after the last period in the standard model, so the interval from conception is 266 days, and an ultrasound that measures a gestational age converts by adding the remainder of the 280 days to the scan date.
The page also lists milestone dates from the same count: the end of the first trimester at 13 weeks 6 days, the end of the second at 27 weeks 6 days, and the current gestational age in weeks and days for any chosen date. These are calendar positions derived from the 280-day convention, printed as dates and week counts only.
A due date from any of these methods is an estimated date produced by a counting convention, for information only. Actual dating and all pregnancy care are matters for the clinicians providing that care, and an ultrasound dating assessment can supersede a period-based date.
Worked examples
Last period, 32-day cycle
- Input
- First day of last period = 15 Jan 2026, Cycle = 32 days
- Working
- Adjustment = 32 − 28 = +4 days, so the count is 284 days: 15 Jan 2026 + 284 days = 26 Oct 2026.
- Result
- Due date = 26 Oct 2026
From an ultrasound scan
- Input
- Scan date = 10 Nov 2026, Gestational age at scan = 8 weeks 0 days (56 days)
- Working
- Remaining = 280 − 56 = 224 days. Due date = 10 Nov 2026 + 224 days = 22 Jun 2027.
- Result
- Due date = 22 Jun 2027
Frequently asked questions
What is Naegele's rule?
The standard dating convention that counts 280 days (40 weeks) from the first day of the last menstrual period for a 28-day cycle, adjusting day for day when the cycle is longer or shorter than 28 days.
How is gestational age counted on a given date?
As elapsed days from the first day of the last period, expressed in weeks and remaining days. For the first worked example, 30 Jan 2027 is 137 days after 15 Sep 2026, which is 19 weeks 4 days.
Why do the period and ultrasound methods agree in the examples?
Because the scan example was constructed on the same pregnancy: a scan on 10 Nov 2026 measuring 8 weeks 0 days implies the same start date as a 15 Sep 2026 last period, so both counts land on 22 Jun 2027. In practice the two methods can differ by several days.
Is this a substitute for clinical dating?
No. This page applies a published counting convention to dates entered, for information only. Pregnancy dating and care are provided by clinicians, and a clinical ultrasound assessment can revise a period-based date.
Are dates stored?
No. The calculation runs entirely in the browser. Dates entered are never uploaded, stored or tracked.
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