Due date method: 280 days from your last period

Naegele 280 days in plain words

The rule takes the first day of your last period and adds 280 days. That span is 40 weeks. It presumes a 28 day cycle with release near day 14, but the due date stays at last period plus 280 days even if your cycle runs long or short.

Try it on paper. Last period Jan 1 plus 280 days lands near Oct 8. Type the same date in the free date tool to see the same answer plus week count. Real due dates shift with scan results. Use this date as a start for plans, not as a set day.

What each trimester means

Weeks 1 to 13 are the first trimester. Weeks 14 to 27 are the second. Week 28 on is the third. The tool turns those weeks into date spans from your start date. That helps you plan visits, leave, and baby gear buys by week.

Week count starts at week 1 on the last period date. Pick any date to see weeks and days since then. A result like 20 weeks and 3 days tells you where you sit in the three spans. Keep in mind care needs shift by person, so dates alone do not set care steps.

Leap safe: Feb 29 and odd months

The math counts true calendar days. That means leap days need no fix up. A start of Feb 29 still adds 280 real days and lands right. Short months land right too. Years 1900 to 2100 all work the same way.

Cycle length still moves the fertile window and next period date. Type your true length from 15 to 60 days. The due date holds at plus 280. Results are calendar math only. This is not medical advice, a diagnosis, or care advice. Talk to your doctor about your health. For loan math in plain words, see our loan monthly payment formula guide.