Pregnancy Due Date

Pregnancy Due Date helps you explore the stated health question. Start with the labelled inputs, then review the method, worked example and limitations before using a result.

Enter your values in the calculator fields to get an instant result.

Calculator guide

Pregnancy Due Date helps you explore the stated health question. Start with the labelled inputs, then review the method, worked example and limitations before using a result.

Formula or method

A last-menstrual-period estimate adds approximately 280 days to the first day of the last period, with any displayed cycle-length adjustment.

How to use this calculator

  1. Enter the first day of the last menstrual period and the cycle length.
  2. Check the estimated date with your clinician; ultrasound dating may take priority.

Worked example

For a last period starting January 1, 2026, a 280-day estimate gives October 8, 2026 before any cycle adjustment.

Understanding the result

Compare the output with the pregnancy due date worked example using exactly the same inputs. A different assumption or rounding convention can produce a different displayed result; the output does not establish personal or professional suitability.

Limitations and assumptions

  • Due dates are estimates, not guaranteed delivery dates. Ultrasound and clinician assessment may revise dating, especially with irregular cycles.
  • The worked example demonstrates the stated assumptions, not a recommendation about your personal circumstances.

Frequently asked questions

Which inputs should I check first?

Follow the Pregnancy Due Date input instructions above. Check each measurement, date, selection or expression before comparing results.

Why might my result differ from another tool?

Compare the other tool's pregnancy due date method, input units, rounding and assumptions. A matching title does not guarantee that both tools answer the same question.

Does a linked reference certify this result?

No. A reference can explain a formula or provide background for Pregnancy Due Date, but it does not endorse this website, validate personal inputs or establish professional suitability.

Sources

Educational and planning information only. Sources are attributed background or formula references, not endorsements. Verify consequential decisions with an appropriate qualified professional.