Explain it like I'm 12
The due date calculator adds 280 days to the last menstrual period date, with a simple cycle-length adjustment and gestational-age count.
Health & Lifecycle
Pregnancy Due Date Calculator
Estimate due date, gestational age and trimester from last menstrual period date using the standard 280-day convention.
Calculator
Working calculator
Live result2027-03-082 weeks 5 days as of 2026-06-20 · first trimester estimate · cycle adjustment +0 days.
Formula used
Estimated due date = LMP date + 280 days + (cycle length − 28 days). Gestational age = as-of date − LMP date.
This is the method behind the answer, so the result can be checked rather than simply trusted.Visual grid
This number is one point on a larger pattern
Pregnancy Due Date is not just a final answer. It is a step on a line: before and after, input and output, assumption and result.
Micro-timehours, minutes, shiftsHuman scaledays, weeks, projectsMacro-timemonths, years, calendars
InputFormulaResult
2027-03-08CalculationTime keeps the path visible: the input, the method and the final number belong together.
CalculationTime
Pregnancy Due Date Calculation Report
2027-03-082 weeks 5 days as of 2026-06-20 · first trimester estimate · cycle adjustment +0 days.
Inputs
- LMP year
- 2,026
- LMP month
- 6
- LMP day
- 1
- As-of year
- 2,026
- As-of month
- 6
- As-of day
- 20
- Cycle length
- 28 days
Method
Estimated due date = LMP date + 280 days + (cycle length − 28 days). Gestational age = as-of date − LMP date.
- For an LMP date of 2026-06-01 and 28-day cycle, the estimated due date is 2027-03-08.
Assumptions
- This is a conventional estimate only.
- Ultrasound dating and clinical advice can change the estimated due date.
- Dates are handled as UTC calendar days to avoid timezone drift.
Notes
Use this space on the printed report for client, supplier, classroom, job-location, measurement, quote or approval notes.
Source references
- ACOG Methods for Estimating the Due Date — clinical due-date method reference
Formula
Estimated due date = LMP date + 280 days + (cycle length − 28 days). Gestational age = as-of date − LMP date.
Worked example
For an LMP date of 2026-06-01 and 28-day cycle, the estimated due date is 2027-03-08.
Professional note
Master’s Tip: treat the due date as an estimate window, not a guaranteed delivery day.
Regional and unit assumptions
Common 280-day LMP method. Clinical pregnancy dating should be confirmed with a qualified health professional.
Assumptions and limitations
- This is a conventional estimate only.
- Ultrasound dating and clinical advice can change the estimated due date.
- Dates are handled as UTC calendar days to avoid timezone drift.
Methodology & Accuracy
How this calculator is checked
CalculationTime pages are built around visible arithmetic: the formula, assumptions, worked example and practical limitations are shown so the result can be checked rather than simply trusted.
Formula used
Estimated due date = LMP date + 280 days + (cycle length − 28 days). Gestational age = as-of date − LMP date.
Standard or basis
Common 280-day LMP method. Clinical pregnancy dating should be confirmed with a qualified health professional.
Where a calculator follows a named legal, trade or industry standard, that standard is cited visibly. Otherwise the page uses transparent general arithmetic and states its limits.Master's Tip
Master’s Tip: treat the due date as an estimate window, not a guaranteed delivery day.
Related calculators
Questions
Why add 280 days?
The common LMP convention estimates pregnancy at about 40 weeks from the first day of the last menstrual period.
Can ultrasound change the date?
Yes. Clinicians may revise the estimated due date based on ultrasound and medical history.