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Due Date Calculator

Estimate your pregnancy due date from your last menstrual period and cycle length.

Last updated: June 13, 2026

Calculator

Days Since First Day of Last Period

Average Cycle Length

days

Results

Gestational Age4w 2d

1st Trimester

Time Remaining~35 weeks (250 days)

Progress10.7%

of ~40 weeks

Estimated OvulationDay 14 of cycle

~16 days ago

Current Trimester1st Trimester

How to Use This Calculator

1Enter how many days since the first day of your last menstrual period.
2Enter your average cycle length in days (default 28).
3View your gestational age, trimester, time remaining, and pregnancy progress.
4Adjust cycle length if your cycles are longer or shorter than 28 days.

Formula Explanation

Due date is estimated using Naegele's Rule: add 280 days (40 weeks) to the first day of the last menstrual period (LMP), adjusted for cycle length. If your cycle is longer than 28 days, ovulation occurs later, shifting the due date forward.

Due Date = LMP + 280 days + (Cycle Length - 28) Gestational Age = Days since LMP Trimester: 1st (weeks 1-12), 2nd (13-26), 3rd (27-40)

Variables:

Days Since LMPNumber of days since the first day of your last period

Cycle LengthAverage menstrual cycle length in days (typically 21-35)

280 daysStandard pregnancy length (40 weeks) from LMP

Worked Examples

30 days since LMP, 28-day cycle

1. Gestational age = 30 days = 4 weeks 2 days
2. Due date = 280 - 30 = 250 days remaining
3. Trimester: 1st (week 4)

Result: 4 weeks 2 days pregnant, 1st trimester, ~250 days to go

90 days since LMP, 32-day cycle

1. Gestational age = 90 days = 12 weeks 6 days
2. Adjusted total = 280 + (32-28) = 284 days
3. Days remaining = 284 - 90 = 194

Result: 12 weeks 6 days, end of 1st trimester, ~194 days remaining

Why Use This Calculator

Track your pregnancy week-by-week from the first day of your last period.
Adjusts for irregular cycle lengths — not everyone has a 28-day cycle.
Shows your current trimester and pregnancy progress percentage.
No signup required — instant, private results.

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Tips & Best Practices

Only about 5% of babies are born on their exact due date — it is an estimate, not a guarantee.
First-trimester ultrasound dating is more accurate than LMP calculation.
Track your cycle for 3-6 months before pregnancy for a more accurate average.
Your provider may adjust your due date based on ultrasound measurements.

Common Mistakes to Avoid

❌ Using the wrong date for LMP.

✅ LMP is the FIRST day of your LAST period — not the last day, and not when it ended.

❌ Assuming a 28-day cycle when yours is different.

✅ If your cycles are regularly 32 days, enter 32. This shifts ovulation and due date by 4 days.

❌ Panicking when delivery date differs from due date.

✅ Full-term is 37-42 weeks. Most babies arrive within 2 weeks before or after the estimated due date.

Frequently Asked Questions

How accurate is a due date calculator?

LMP-based calculations are accurate to within about 2 weeks. First-trimester ultrasound is accurate to within 3-5 days. Only about 5% of babies arrive on the exact estimated date.

What if I don't know my last period date?

An early ultrasound (ideally before 12 weeks) can accurately date your pregnancy by measuring the baby's crown-rump length. Contact your healthcare provider.

Does cycle length affect my due date?

Yes. If your cycle is 35 days instead of 28, you likely ovulated on day 21 instead of day 14. This shifts your true due date about 7 days later than a standard calculation would show.

When should I see a doctor to confirm my due date?

Schedule your first prenatal visit at 8-10 weeks. A first-trimester ultrasound provides the most accurate dating and can confirm or adjust the LMP-based estimate.

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Embed This Calculator

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<iframe src="https://redicalc.com/embed/health/due-date-calculator" width="100%" height="600" style="border:none;border-radius:12px;box-shadow:0 1px 3px rgba(0,0,0,0.1);" title="Due Date Calculator — RediCalc.com" loading="lazy" allowtransparency="true"></iframe>

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Disclaimer: This calculator is provided for informational and educational purposes only. Results are estimates and should not be used as a substitute for professional advice. RediCalc.com makes no guarantees regarding the accuracy, completeness, or suitability of any calculations. Always consult a qualified professional before making financial, health, construction, or other important decisions.

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