Calculate Gestational Age
What this pregnancy gestational age calculator does
This tool estimates how far along a pregnancy is in weeks and days, using the first day of your last menstrual period (LMP), your average cycle length, and the date you want to calculate from (usually today). It also estimates your expected due date and shows which trimester you are in.
Clinics typically date pregnancy in gestational weeks, not from conception day. That means pregnancy week count starts about two weeks before ovulation in a standard 28-day cycle.
How gestational age is measured
1) LMP-based dating
Most early pregnancy dating starts with LMP. In a 28-day cycle, ovulation is often around day 14, so gestational age is usually about 2 weeks ahead of embryonic/fetal age in very early pregnancy.
2) Ultrasound-based dating
Early ultrasound can refine due date estimates, especially if cycles are irregular or the LMP is uncertain. If ultrasound and LMP dating differ, your clinician may adjust your estimated due date.
3) Why cycle length matters
If your cycle is longer or shorter than 28 days, ovulation may occur later or earlier. This calculator adjusts dates by your cycle difference to provide a more personalized estimate.
How to use this calculator
- Enter the first day of your last period.
- Choose the date you want to calculate gestational age for (defaults to today).
- Enter your typical cycle length (28 is default).
- Click Calculate to see weeks/days, trimester, and estimated due date.
Understanding your results
Your result includes:
- Gestational age: weeks and days pregnant
- Estimated due date (EDD): LMP + 280 days (adjusted by cycle length)
- Trimester: first, second, or third trimester
- Time to due date: days remaining or days past EDD
Important notes and limitations
- This is an estimate, not a diagnosis.
- Irregular cycles, uncertain LMP, breastfeeding, recent hormonal contraception, or fertility treatment can affect accuracy.
- In IVF pregnancies, dates are usually calculated from embryo transfer and should follow clinic guidance.
- Always use your prenatal provider's official due date for medical decisions.
Common questions
Is gestational age the same as fetal age?
No. Gestational age is counted from LMP, while fetal age starts near conception (typically about 2 weeks later in a 28-day cycle).
Can my due date change?
Yes. Early ultrasound may shift your due date if growth measurements suggest a different gestational age than LMP-based dating.
What if I do not know my exact LMP date?
Use your best estimate, then confirm with a healthcare professional. Early ultrasound is often most helpful in this case.
When to contact your healthcare provider urgently
Seek urgent medical care for severe abdominal pain, heavy bleeding, fainting, fever, severe headache, vision changes, or reduced fetal movements later in pregnancy. If anything feels wrong, contact your provider immediately.
Medical disclaimer: This content is for educational purposes and does not replace professional medical advice, diagnosis, or treatment.