Enter your last period or due date to see your current gestational week, trimester, days until your due date, and a size comparison for this stage.
"Weeks pregnant" is measured from the first day of your last menstrual period (LMP), not from conception. Since ovulation and conception typically occur around day 14 of a cycle, you are already recorded as roughly two weeks pregnant before conception has actually taken place. It is a deliberate convention, not an error — the LMP date is the one most people know precisely, while the conception date usually is not.
The formula is simple once you accept that starting point: week = (today − LMP) ÷ 7, rounded down, and due date = LMP + 280 days (40 weeks). If you only know the due date, this calculator runs that second formula backwards to recover an LMP, then proceeds identically.
LMP of 1 January 2026, checked on 15 April 2026: that is 104 days elapsed, giving week 14 — the first day of the second trimester on this page’s boundaries. The due date is 8 October 2026, which is 176 days away from the check date.
This calculator draws them at weeks 1–13, 14–27, and 28 onward. Those are common boundaries, not a universal standard — some clinical sources split at 12/13 and 27/28 instead, so do not be surprised if your provider's chart is off by a week from this one. The size comparisons follow the same LMP-based week number, so a listed "week 14" size assumes the standard dating convention above.
The 280-day, 40-week figure is an average built into the arithmetic, not a prediction for any individual pregnancy. Only a minority of births land exactly on the calculated due date; cycle length, the actual timing of ovulation within a cycle, and dating-scan measurements can each shift the real timeline by days to over a week in either direction. Where an ultrasound estimate and this LMP-based estimate disagree, clinical practice generally defers to the scan. This tool is for tracking and general information, not a diagnosis or a substitute for antenatal care — see the due date calculator for the same 280-day model from the opposite direction, and the pregnancy weight gain calculator once you know your week.
From your last menstrual period (LMP), current week = number of days since the first day of your LMP, divided by 7, rounded down. If you instead know your due date, this calculator first back-calculates an equivalent LMP (due date minus 280 days) and then works from that same rule — the same math the Pregnancy Due Date Calculator uses in reverse.
Medical convention counts gestational age from the first day of the last menstrual period because that date is usually known with reasonable precision, while the exact conception date rarely is. Conception typically happens about two weeks after LMP, so you're considered a couple of weeks "pregnant" before conception technically occurs — standard practice, not an error.
The Pregnancy Due Date Calculator focuses on calculating and confirming your due date from several possible starting points — LMP, a known conception date, or an IVF transfer date. This tool assumes you already have one of those dates and instead focuses on week-by-week progress right now: your current gestational week, trimester, days remaining, and an illustrative size comparison for this stage of the pregnancy.
No — fruit and vegetable size comparisons are illustrative and popular in pregnancy apps and books, but actual fetal size varies meaningfully from pregnancy to pregnancy. Your provider's ultrasound measurements are the accurate source for size and growth tracking, not a produce-aisle comparison.
Worked example: an LMP of March 10 checked on July 16 is 128 days later, or floor(128 ÷ 7) = 18 completed weeks — squarely in the second trimester, with a due date of December 15 (LMP + 280 days) about 152 days away at that point, and a size comparison of roughly "lemon to banana" for the week-14-to-20 range.
Need to confirm your due date first? See the Pregnancy Due Date Calculator. Before pregnancy, the Period Calculator forecasts cycles and the Ovulation Calculator identifies the fertile window.