How accurate is the due date calculator?

This calculator uses the medically established Naegele's Rule and Mittendorf-Williams rule for cycle adjustment, giving 99.99% calculation accuracy. Only 4% of babies are born exactly on the due date — a normal delivery occurs between week 37 and 42.

Pregnancy is divided into three trimesters: First (Weeks 1–13), Second (Weeks 14–27), and Third (Weeks 28–40).

Can I calculate from conception date?

Yes. Select 'Conception Date' as your method and enter the date. The calculator adds 266 days (38 weeks) to find your EDD.

What if my cycle is not 28 days?

Enter your actual average cycle length. The calculator adjusts the due date accordingly — each day your cycle differs from 28 days shifts the EDD by one day.

Is this pregnancy calculator free?

Yes, 100% free. No signup required. All calculations run entirely in your browser — no data is stored or uploaded.

What is the difference between gestational age and fetal age?

Gestational age counts from the first day of your LMP — this is what doctors use. Fetal age (embryonic age) counts from conception, which is about 2 weeks less than gestational age.

Free Tool · No Signup · 99.99% Accurate

Pregnancy Calculator 🤰

Calculate your due date, how many weeks pregnant you are, your trimester, and all key pregnancy milestones — from your Last Menstrual Period (LMP) or conception date.

First Day of Last Period

Cycle Length (days)

Estimated Due Date (EDD)

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Weeks Pregnant

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Days Pregnant

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Days Until Due

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Trimester

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Conception Date

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Fetal Age (wks)

Pregnancy Progress

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of 40 weeks

🗓 Key Milestones

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How to Use the Pregnancy Calculator

Choose Your Method

Select "Last Menstrual Period" if you know when your last period started. Select "Conception Date" if you know when conception occurred.

Enter Your Date

For LMP, enter the first day of your last menstrual period. For conception method, enter the date of conception.

Set Cycle Length (LMP only)

Select your average menstrual cycle length. The default is 28 days. Adjusting this improves due date accuracy for irregular cycles.

Click Calculate

Press "Calculate Pregnancy" to instantly see your due date, weeks pregnant, trimester, and all major milestones.

Review Results

See your EDD, current week, days remaining, trimester progress bar, and a complete milestone timeline with estimated dates.

About This Pregnancy Calculator

TheAshNow Pregnancy Calculator uses medically established formulas to calculate your Estimated Due Date (EDD) with the highest possible accuracy. All calculations run entirely in your browser — no data is uploaded or stored.

Naegele's Rule (LMP Method)

The standard due date formula used worldwide by OBGYNs: add 280 days (40 weeks) to the first day of your Last Menstrual Period. This assumes a 28-day cycle. Our calculator automatically adjusts for your actual cycle length — each day your cycle differs from 28 shifts the EDD by one day.

Conception Date Method

If you know your conception date (e.g. from IVF or ovulation tracking), the calculator adds 266 days (38 weeks) to find your EDD. This is equivalent to gestational week 2 being the conception point in an average 28-day cycle.

Gestational Age vs. Fetal Age

Gestational age (what doctors use) counts from the first day of LMP. Fetal age counts from conception — approximately 2 weeks less. Both are shown in your results.

Normal Delivery Window

Only about 4% of babies are born exactly on the EDD. A full-term delivery is considered normal between Week 37 and Week 42. The calculator shows the full normal window alongside your EDD.

Accuracy Note

This tool calculates a mathematical EDD based on the dates you provide. For medical confirmation of gestational age and due date, always rely on an ultrasound and your healthcare provider's assessment.

Frequently Asked Questions

Using Naegele's Rule: add 280 days to the first day of your Last Menstrual Period. If your cycle differs from 28 days, the due date shifts accordingly — one day per day of difference. For conception date, 266 days are added.

The mathematical calculation is 99.99% accurate based on the dates you enter. It uses Naegele's Rule with cycle-length adjustment — the same method used by doctors. Remember: only 4% of babies arrive exactly on the EDD; delivery between weeks 37–42 is normal.

First Trimester: Weeks 1–13. Second Trimester: Weeks 14–27. Third Trimester: Weeks 28–40 (until delivery). The calculator shows which trimester you are in and how far along you are within it.

Yes. Select your average cycle length from the dropdown. The due date will adjust accordingly. For highly irregular cycles, an early ultrasound (6–10 weeks) gives the most accurate gestational age.

Gestational age is counted from LMP (what your doctor reports). Fetal age is counted from actual conception — roughly 2 weeks less than gestational age. Both are shown in your results.

Yes, 100% free. No signup, no registration. All calculations happen in your browser — no personal data is collected or stored.

As soon as you suspect or confirm pregnancy. This calculator is an informational tool only — it does not replace medical care. Book your first prenatal appointment (ideally before 10 weeks) with your healthcare provider.