By Zencalcy Editorial TeamLast reviewed About us
This calculator reports gestational age on a specific date rather than today, which is useful for reviewing a scan date, a symptom diary or a past appointment. It counts from the first day of the last menstrual period and returns weeks and days, the trimester and an estimated due date. It assumes a 28-day cycle because no cycle field is used here.
Gestational age on any date from the LMP.
Gestational age = date to check − LMP EDD = LMP + 280 days
The calculation assumes a 28-day cycle and ovulation around day 14. A longer or shorter cycle shifts the true gestational age, so the result is an estimate. The due date shown is the conventional 40-week LMP-based date and may differ from an ultrasound-derived date.
| Symbol | Meaning |
|---|---|
| LMP | First day of the last menstrual period. |
| Check date | The date whose gestational age you want. |
| GA | Weeks and days pregnant on that date. |
The interval is 204 days, which is 29 weeks 1 day. That falls in the third trimester. The estimated due date is 1 January 2026 + 280 days = 8 October 2026. Checking 12 March 2026 instead gives 70 days, or 10 weeks 0 days, in the first trimester.
Pregnancy records are full of dates: scan appointments, blood tests, symptom notes and milestone photos. Knowing the gestational age on each of those dates makes the record easier to interpret later. It also helps when someone wants to understand a past ultrasound report or compare a fundal-height measurement with the weeks recorded at the time. The arithmetic is simple, but the assumption is not neutral: counting from the LMP treats every cycle as if ovulation happened on day 14. For someone with irregular or long cycles, the result may be several days ahead of the true age. An early dating scan resolves most of that uncertainty. Use this page for orientation and record-keeping, and rely on your maternity team for the official dates that guide care.
Continue with the Pregnancy Weight Gain Calculator, Gestational Age Calculator, or the Conception Date Calculator — or browse more gynecology & pregnancy tools and all health calculators.
Also see the Ovulation Calculator and the Pregnancy Due Date Calculator.
The page has no cycle-length field, so it uses the standard 28-day assumption. If your cycles are consistently longer or shorter, the true gestational age may differ by several days. Use the gestational age calculator for a cycle-adjusted estimate.
Pregnancy dating and fertility estimates assume regular cycles and typical ovulation. They cannot confirm pregnancy, viability or gestational age, and they do not replace ultrasound or prenatal care. Seek urgent care for pain, bleeding or reduced fetal movement.
Reference material used to build and check this calculator:
Last reviewed: September 2026. See how we build and check every tool on the about page.
Content updated: September 2026