The first sum most people do on learning they’re pregnant is the due date. The Government of Jersey’s pregnancy guidance works it out by adding 280 days (40 weeks) to the first day of your last period, assuming a 28-day cycle, and says it’s only a rough guide; the 12-week scan gives a more accurate date. If your last period started on 1 April 2026, the due date is 6 January 2027. Enter a date below for the due date and how far along you are.
1. Due date = first day of last period + 280 days (40 weeks).
2. It assumes a 28-day cycle and is a rough guide. A different cycle may shift it (our gloss).
3. The 12-week scan gives a more accurate date.
Updates as you type. The due date is the Government of Jersey’s “first day of your last period + 280 days (40 weeks)”, assuming a 28-day cycle — a rough guide; the 12-week scan gives a more accurate date. The “around 12 weeks” date is start + 84 days (our working).
How it’s worked out — Government of Jersey
| Type | What the source says | Worth noting (ours) |
|---|---|---|
| Sum | First day of last period + 280 days (40 weeks) | — |
| Assumption | A 28-day cycle | — |
| Status | Only a rough guide | — |
| More accurate | The 12-week scan in antenatal care | — |
Reading the calculator — our notes
- Estimated due date — the first day of the last period plus 280 days, exactly as the source sums it.
- Weeks on the reference date — days from the start to the reference date, divided by 7: the quotient is weeks, the remainder days. 201 days is 28 weeks 5 days.
- Days to the due date — days left from the reference date; past the due date it shows “days past”.
- Around 12 weeks — start + 84 days (12 weeks), putting the source’s 12-week scan on the calendar.
With real dates — our examples
| Last period started (example) | + 280 days = due date | Worth noting (ours) |
|---|---|---|
| 1 April 2026 | 6 January 2027 | — |
| 1 May 2026 | 5 February 2027 | — |
| 1 February 2026 | 8 November 2026 | — |
These dates are our examples to check the sum. “Weeks” are days since the period started, divided by 7 (our working).
Reading the due date
A due date is an estimate from a sum, not the day the baby will arrive. This page calls it a rough guide and gives no figures on how many babies arrive on the day or on the term range, and we haven’t added any.
Korean pregnancy and birth support is covered in child allowance, parental leave and the maternity leave benefit calculator.
Checklist
- ☐ Enter the first day of your last period
- ☐ Due date = start + 280 days
- ☐ A cycle other than 28 days may shift it
- ☐ Confirm with the 12-week scan
Questions that remain
My cycle is 35 days. What then?
This page only says it assumes a 28-day cycle and gives no adjustment. Go by the date from your scan.
Do Korean clinics use the same method?
We didn’t read Korean guidance this time. The due date set by your obstetric clinic is the one to use (our pointer).
Sources
- Government of Jersey — Working out your due date — source (no published or updated date shown; checked 19 October 2026). +280 days (40 weeks), 28-day cycle, rough guide, 12-week scan.
- Not read. Korean agency due date guidance; on-time birth rates and term ranges.
- What we added. The “worth noting” column and the Korean everyday gloss.
Where else to check
- Your obstetric clinic — the scan-based due date.
Written on 19 October 2026. The content is from the source; the glosses are ours.
