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Due Date Calculator

Use this due date calculator to review an educational health calculation for due date.

Primary answer
Estimated due date
Inputs to verify
Dating method, First day of last period, and Regular cycle length
Use type
Use as a review-only estimate; verify before relying on it.
Keyword intent
due date calculator

Calculator

Due Date Calculator

Calculates estimated due date from dating method, first day of last period, regular cycle length. Defaults are filled in so you can review a working example before changing inputs.

Choose whether to estimate from the first day of the last period or a known conception date.

Required for LMP mode. Use a real Gregorian calendar date in YYYY-MM-DD format.

days

Required for LMP mode. This estimate assumes a regular cycle.

Required for conception mode. Spontaneous conception dates are usually estimates.

Used to estimate current gestational age and days until due date.

Result

Result reflects the current submitted inputs.

  • Risk C
  • Reviewed 2026-05-26
  • 4 sources
Estimated due date2026-10-08
Gestational age20 weeks
Additional days5 days
Total gestational age145 days
Days until due date135 days
Dating method noteLMP + 280 days + (28 - 28) day regular-cycle adjustment.
Medical noteEducational estimate only; confirm pregnancy dating, screening timing, and care decisions with a qualified health care professional.
  • This calculator is an educational estimate only and is not medical advice.
  • LMP mode assumes accurately recalled first day of last menstrual period and regular menstrual cycles.
  • Conception mode assumes a known conception/fertilization date; spontaneous conception dates are usually not definitive.
  • Ultrasound dating, IVF transfer dates, irregular cycles, pregnancy complications, and clinician redating are not modeled.
  • Calendar math is date-only; time zones and times of day are ignored.

Accuracy notes

Risk level
C
Reviewed
2026-05-26
Sources
4
Primary result
Estimated due date

Formula logic is kept in a pure calculator module with fixtures, source notes, and page-visible assumptions.

High-risk estimate

Educational estimate, not advice

This health calculator is for educational estimates only. It does not diagnose, treat, provide medical clearance, or replace advice from a qualified health professional.

Check the reviewed sources, assumptions, and formula limits before using this result for a financial, health, or safety decision.

Review cadence: 12 months; next review due 2027-05-26.

Categories

What the result means

Estimated due date is the number to carry forward from this due date calculation. Estimated calendar due date from the selected source-backed method. Treat the result as educational context, then read the limitations and assumptions before discussing it with a professional. Use gestational age, additional days, and total gestational age to explain why estimated due date moved when an input changed. Record the inputs you used and verify any health concern with a qualified professional.

Estimated due dateEstimated calendar due date from the selected source-backed method.
Gestational ageCompleted gestational weeks as of the selected date.
Additional daysDays beyond the completed gestational weeks.
Total gestational ageTotal estimated gestational days as of the selected date.

Use the result this way

  1. Start with Estimated due date, then use supporting outputs only to explain the primary answer.
  2. Verify dating method, first day of last period, and regular cycle length before copying the result.
  3. Choose the mode or method first because it can change which formula is applied, keep units consistent with the labels shown in the form, and confirm the date, time, and endpoint convention before comparing results.
  4. Record the inputs you used and verify any health concern with a qualified professional.

User job

How to use this calculator

Use Due Date Calculator when you need estimated due date, then use gestational age and additional days to check the context for general wellness education and preparing for a professional conversation.

Best for

  • Understanding a formula-based estimate
  • Seeing which inputs drive a health-related output
  • Reviewing a default example before entering your own dating method and first day of last period.

Check before relying

  • Health formulas can be population-specific; do not use the result as diagnosis or treatment advice.
  • This calculator is an educational estimate only and is not medical advice.
  • LMP mode assumes accurately recalled first day of last menstrual period and regular menstrual cycles.
  • Source context: Merck Manual Professional Edition, reviewed 2026-05-26.

Next useful step

  • Pregnancy CalculatorUse next when the pregnancy comparison needs pregnancy inputs such as first day of last period and regular cycle length.
  • Pregnancy Conception CalculatorUse next when the pregnancy task needs estimated conception date instead of estimated due date.
  • Ovulation CalculatorUse next when the pregnancy task needs estimated ovulation date instead of estimated due date.

Limits of this estimate

  • Supports educational date estimation only; it excludes ultrasound dating, IVF transfer protocols, irregular cycles, pregnancy complications, clinician redating, and clinical scheduling decisions.
  • The result depends on user-entered inputs and the documented assumptions; defaults are examples only.
  • Search indexing approval does not downgrade this page from risk level C or turn the result into professional advice.

Formula

LMP mode estimates EDD as LMP + 280 days plus regular-cycle adjustment. Conception mode estimates EDD as conception date + 266 days. Key assumptions: This calculator is an educational estimate only and is not medical advice. LMP mode assumes accurately recalled first day of last menstrual period and regular menstrual cycles. Conception mode assumes a known conception/fertilization date; spontaneous conception dates are usually not definitive.

  • LMP mode estimates EDD as LMP + 280 days plus regular-cycle adjustment. Conception mode estimates EDD as conception date + 266 days.
  • This calculator is an educational estimate only and is not medical advice.
  • LMP mode assumes accurately recalled first day of last menstrual period and regular menstrual cycles.
  • Primary source context: Merck Manual Professional Edition.

Inputs

Enter dating method, first day of last period, regular cycle length, and conception date for general wellness education and preparation for a professional conversation. Before calculating, choose the mode or method first because it can change which formula is applied, keep units consistent with the labels shown in the form, and confirm the date, time, and endpoint convention before comparing results. Dating method: Choose whether to estimate from the first day of the last period or a known conception date. First day of last period: Required for LMP mode. Use a real Gregorian calendar date in YYYY-MM-DD format. Regular cycle length: Required for LMP mode.

Dating methodChoose whether to estimate from the first day of the last period or a known conception date.
First day of last periodRequired for LMP mode. Use a real Gregorian calendar date in YYYY-MM-DD format.
Regular cycle lengthRequired for LMP mode. This estimate assumes a regular cycle.
Conception dateRequired for conception mode. Spontaneous conception dates are usually estimates.
Calculate as ofUsed to estimate current gestational age and days until due date.

Example

Using the default inputs, Due Date Calculator returns estimated due date of 2026-10-08. Adjust dating method, first day of last period, regular cycle length, and conception date to match your own scenario.

FAQ

How is estimated due date calculated here?

LMP mode estimates EDD as LMP + 280 days plus regular-cycle adjustment. Conception mode estimates EDD as conception date + 266 days. The first assumption to check is: This calculator is an educational estimate only and is not medical advice.

What does Estimated due date mean for due date?

Treat the result as educational context, then read the limitations and assumptions before discussing it with a professional. Secondary values such as gestational age, additional days, and total gestational age are there to explain the primary answer, not to replace it.

What should I enter for Dating method?

Choose whether to estimate from the first day of the last period or a known conception date. Choose the mode or method first because it can change which formula is applied, keep units consistent with the labels shown in the form, and confirm the date, time, and endpoint convention before comparing results.

How does First day of last period change estimated due date?

Required for LMP mode. Use a real Gregorian calendar date in YYYY-MM-DD format. Changing it can alter estimated due date because the formula uses the submitted inputs together. Also compare measurement method, formula population, age range, units, sex or activity assumptions, and clinical context.

Why does the due date example show 2026-10-08 for estimated due date?

The default inputs produce 2026-10-08 for estimated due date. Treat that as a format and scale check, then replace every default value with your own inputs.

Can the due date result diagnose or prescribe anything?

No. Use it as educational context only. Health formulas can depend on population, measurement method, age range, and clinical context.

Sources

Last reviewed: 2026-05-26

  • reputableReviewed 2026-05-26 · Source Modified Feb 2025
    Gestational AgeMerck Manual Professional Edition. EDD formulas: conception date + 266 days, LMP + 280 days for regular 28-day cycles, and LMP + 280 + (cycle length - 28) for other regular cycles; ultrasound redating caveats.
    Scope
    Professional medical reference covering gestational age and estimated date of delivery formulas.
    Supports
    EDD formulas: conception date + 266 days, LMP + 280 days for regular 28-day cycles, and LMP + 280 + (cycle length - 28) for other regular cycles; ultrasound redating caveats.
    Limits
    Supports educational date estimation only; it excludes ultrasound dating, IVF transfer protocols, irregular cycles, pregnancy complications, clinician redating, and clinical scheduling decisions.
  • reputableReviewed 2026-05-26 · Source Modified Sept 2024
    Pregnancy Test and Due DateMerck Manual Consumer Version. 280-day LMP estimate, 266-day conception estimate, January 1 to October 8 example, and estimate limitations.
    Scope
    Consumer medical reference on due date estimates, pregnancy duration, gestational age, and trimester definitions.
    Supports
    280-day LMP estimate, 266-day conception estimate, January 1 to October 8 example, and estimate limitations.
    Limits
    Supports educational date estimation only; it excludes ultrasound dating, IVF transfer protocols, irregular cycles, pregnancy complications, clinician redating, and clinical scheduling decisions.
  • officialReviewed 2026-05-26 · Source Updated 2022
    Pregnancy DatingNCBI Bookshelf / StatPearls. 280-day Naegele-style dating, 28-day cycle assumption, and limitation that clinicians establish pregnancy dating.
    Scope
    Clinical overview of pregnancy dating methods and ACOG-based ultrasound redating thresholds.
    Supports
    280-day Naegele-style dating, 28-day cycle assumption, and limitation that clinicians establish pregnancy dating.
    Limits
    Supports educational date estimation only; it excludes ultrasound dating, IVF transfer protocols, irregular cycles, pregnancy complications, clinician redating, and clinical scheduling decisions.
  • officialReviewed 2026-05-26 · Source May 2017, reaffirmed 2024
    Methods for Estimating the Due DateAmerican College of Obstetricians and Gynecologists / Society for Maternal-Fetal Medicine. Medical limitation context for estimated due dates and clinician review.
    Scope
    Professional guidance on pregnancy due-date estimation and documentation.
    Supports
    Medical limitation context for estimated due dates and clinician review.
    Limits
    Does not make this calculator a clinical dating tool; ultrasound, IVF, irregular cycles, and clinician-established dating remain outside this implementation.

Disclaimer

This health calculator is for educational estimates only. It does not diagnose, treat, provide medical clearance, or replace advice from a qualified health professional.