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Due Date Calculator

Estimate your baby's due date and key pregnancy milestones. Choose to calculate from your last menstrual period, your conception date, or an IVF transfer date.

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How Due Date Calculation Works

The most common method for estimating a due date is Naegele's rule, which adds 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a 28-day cycle with ovulation occurring on day 14. If your cycle is longer or shorter than 28 days, the calculator adjusts the estimate accordingly, since ovulation likely occurs later or earlier in your cycle.

For IVF pregnancies, the due date is calculated from the embryo transfer date. For a Day 5 blastocyst transfer, the calculator adds 261 days (38 weeks minus 5 days of embryo development). For a Day 3 transfer, it adds 263 days. These calculations align with ACOG guidelines for assisted reproductive technology dating. When a conception date is known, the calculator adds 266 days (38 weeks), since conception typically occurs about 2 weeks after the LMP in a standard cycle.

ACOG recommends that a first-trimester ultrasound, ideally performed between 7 and 13 weeks, be used as the most accurate method for establishing or confirming a due date. Ultrasound dating takes precedence over LMP-based calculations if there is a discrepancy of more than 5 to 7 days. This calculator is a helpful planning tool, but your healthcare provider will give you the most reliable estimate. If you have questions about your pregnancy timeline, speak with your OB-GYN.

FAQ

How accurate is a due date calculator?
LMP-based calculations are a good starting estimate but can be off by a week or more, especially if your cycles are irregular or you ovulated later than day 14. A first-trimester ultrasound is the gold standard for dating accuracy. ACOG notes that only about 5% of babies are born on the exact estimated due date.
What if I do not know the date of my last period?
If you are unsure of your LMP, an early ultrasound is the best way to estimate your due date. Your healthcare provider can measure the embryo or fetus and provide a reliable estimate, especially when performed in the first trimester.
What counts as full term?
According to ACOG, early term is 37 weeks 0 days through 38 weeks 6 days, full term is 39 weeks 0 days through 40 weeks 6 days, late term is 41 weeks 0 days through 41 weeks 6 days, and post term is 42 weeks 0 days and beyond. The healthiest outcomes for babies occur during the full-term window.
Does my cycle length affect my due date?
Yes. If your cycle is longer than 28 days, you likely ovulated later, which means your actual due date may be later than a standard calculation suggests. This calculator accounts for cycle length variation to provide a more personalized estimate.

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