Pregnancy Due Date Calculator
Estimate a due date and gestational calendar age from a last-period start or known conception date, with clear dating assumptions.
YOUR CALCULATION
Result
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Calculation steps
Work through one step at a time or reveal the complete calculation. The steps use your current inputs.
How to calculate
Add the conventional 280 days from period start or 266 days from known conception, then count gestational days relative to the resulting date.
Estimated due date=LMP+280 calendar days, or known conception+266 calendar days
Worked example
A last-period start of 2026-01-21 gives an estimated due date of 2026-10-28 under the conventional 28-day-cycle model. That comparison date is modeled as 40 weeks and 0 days.
Assumptions and input details
Date-only estimate for inputs within 1900–2199, assuming a regular 28-day cycle in last-period mode. No cycle-length adjustment, embryo-transfer dating, ultrasound interpretation or clinical redating is performed. Gestational calendar comparison is limited to day 0–308 for display. Calendar checkpoints are not a care schedule. An estimated date is not a prediction of birth or a pregnancy assessment; antenatal assessment and ultrasound may revise dating. Inputs stay in your browser.
References: ACOG: conventional due-date model and its limitations · NHS: estimated due dates and ultrasound dating
Using this calculator
Can I enter my own problem?
Yes. Replace the example values with your own inputs. The result, calculation steps, tables and applicable diagrams update from those inputs. Blank or invalid values clear the result; example values are never silently substituted for missing inputs.
Are the results exact?
Results use floating-point arithmetic and displayed rounding. Read the formula, assumptions and any stated data precision before interpreting the result.
Is my input uploaded?
The calculation runs in your browser. No account, file upload or external AI service is required. Inputs are not saved between page reloads.
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