Pregnancy weeks calculator
Enter the first day of your last menstrual period (LMP) to estimate gestational age in weeks and days. The due date uses 280 days from the LMP. This is an estimate: cycle length and ovulation vary, and a prenatal clinician may revise dating using your history and ultrasound.
Estimate gestational age
How this estimate works
The tool counts elapsed days from the first day of the LMP, divides them into complete weeks and remaining days, and adds 280 days to estimate a due date. This convention is less reliable when the LMP is unknown or cycles are irregular. The month display is approximate; pregnancy care is tracked in weeks and days.
Prenatal care in Brazil
Brazil’s Ministry of Health advises starting prenatal care as soon as pregnancy is suspected or confirmed, preferably by 12 weeks. Visit timing, tests and ultrasound decisions depend on the person and the care team. If you live elsewhere, follow your local health service guidance.
When to seek medical help
During pregnancy, contact your maternity service or health professional promptly about vaginal bleeding, fluid leakage, severe or persistent pain, severe headache or vision changes, seizures, breathing difficulty, fever, or a clear reduction or absence of fetal movement. This page cannot assess symptoms. Use local emergency services when needed.
Frequently asked questions
Why does pregnancy dating start before conception?
Gestational age is conventionally counted from the first day of the last menstrual period. Ovulation and conception dates can vary and may be unknown, so the LMP is used as a starting reference.
My ultrasound gives a different date. Which one should I use?
A clinician should reconcile your menstrual history and ultrasound. First-trimester ultrasound is the most accurate ultrasound period for establishing or confirming gestational age; do not change your care plan based on this calculator.
What if my cycles are irregular or I do not know my LMP?
The estimate may be less accurate. Tell your prenatal care team; they can assess your history and decide whether ultrasound or another method is appropriate.
Does this calculator give a guaranteed birth date?
No. The due date is an estimate, not a prediction or appointment. Only your care team can advise you about your pregnancy and follow-up.
Official references
The prenatal-care notes refer to Brazilian public-health guidance. These sources do not replace individualized medical advice.