Pregnancy Calculator
Estimate only; check important health decisions with a qualified professional.
2% – 55% reference display (not a diagnosis)
Estimate only; check important health decisions with a qualified professional.
Common questions
How many weeks pregnant am I from my last period?
Pregnancy gestational age is conventionally counted from the first day of the last menstrual period (LMP). Enter that date and the date you want to calculate on to see completed weeks and days.
Why does pregnancy age start before conception?
Obstetric dating usually begins at LMP, approximately two weeks before estimated fertilization in a typical 28-day cycle. Ovulation can happen earlier or later.
Does a 35-day cycle change the estimated due date?
In this calculator, the due-date estimate shifts by seven days compared with a 28-day cycle. Gestational weeks shown are counted from the entered LMP date, so the cycle adjustment does not change that count.
How are the pregnancy trimesters estimated?
This tool uses approximate pregnancy day ranges to label first, second and third trimesters. Clinical sources can use slightly different boundaries.
Can the date I enter be in the past or future?
Yes. Choose a comparison date within the calculator’s supported estimated pregnancy interval to see gestational weeks and days on that date.
Can an ultrasound change my due date?
Yes. A clinician may establish or revise pregnancy dating using a first-trimester ultrasound and other clinical evidence. Use the due date documented by your care team.
Can this calculator confirm a pregnancy?
No. It performs calendar calculations only and cannot confirm a pregnancy or determine fetal health.
Is this calculator accurate with irregular periods?
Period-based dating may be less reliable when cycles are irregular or the LMP date is uncertain. Ask a qualified clinician about appropriate dating.
Related calculators
Learn more
How Many Weeks Pregnant Am I?
This pregnancy week calculator shows gestational age in completed weeks and days. Choose the first day of the last menstrual period (LMP), enter your usual cycle length, then select the date on which to calculate pregnancy age. The result also includes an estimated due date, days remaining and an approximate trimester.
How Pregnancy Weeks and Due Dates Are Calculated
Gestational weeks are counted from the first day of LMP, even though fertilization often occurs later. The typical due-date estimate is LMP + 280 days for a 28-day cycle. This tool adjusts the estimated due date by cycle length − 28 days; that adjustment is an approximation, not proof of ovulation timing.
Example: If LMP began on 1 January 2026, the usual 28-day-cycle estimated due date is 8 October 2026. A 35-day cycle moves this simple due-date estimate to 15 October 2026. The pregnancy-week count still uses the LMP date and the selected comparison date.
Pregnancy Trimester and Dating Limitations
The displayed trimester is a general calendar label, not a clinical finding. Early ultrasound is generally the most accurate method to establish or confirm gestational age. Menstrual dates may be uncertain, especially with irregular cycles, and the clinician-established estimated due date should guide prenatal care.
This page focuses on weeks pregnant from LMP. If your main question is when the baby is due, use the Due Date Calculator. To estimate a past conception window, use the Conception Date Calculator.
Medical reference: ACOG — Methods for Estimating the Due Date. This calculator is educational, does not confirm pregnancy and is not a substitute for prenatal care.