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Pregnancy Calculator

Use this pregnancy calculator to review an educational health calculation for pregnancy.

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

Calculator

Pregnancy Calculator

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

Use the first day of bleeding from the last menstrual period in YYYY-MM-DD format.

days

This estimate assumes regular cycles; irregular cycles need clinician or ultrasound dating.

Used to estimate gestational age and trimester.

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
TrimesterSecond trimester
Days until due date135 days
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.
  • The estimate assumes an accurately recalled first day of last menstrual period and regular menstrual cycles.
  • Ultrasound dating, IVF transfer dates, irregular cycles, pregnancy complications, and clinician redating are not modeled.
  • Trimester labels are based on estimated gestational age and should not be used for clinical scheduling decisions.
  • 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

Use Estimated due date as the headline answer for pregnancy. LMP-based estimated due date adjusted for regular cycle length. 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 dateLMP-based estimated due date adjusted for regular cycle length.
Gestational ageCompleted gestational weeks as of the selected date.
Additional daysDays beyond completed gestational weeks.
Total gestational ageTotal estimated gestational days.

Use the result this way

  1. Start with Estimated due date, then use supporting outputs only to explain the primary answer.
  2. Verify first day of last period, regular cycle length, and calculate as of before copying the result.
  3. Keep units consistent with the labels shown in the form, confirm the date, time, and endpoint convention before comparing results, and stay within the documented minimum and maximum ranges.
  4. Record the inputs you used and verify any health concern with a qualified professional.

User job

How to use this calculator

Use Pregnancy 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 first day of last period and regular cycle length.

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.
  • The estimate assumes an 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

  • Due Date CalculatorUse next when the pregnancy comparison needs due date inputs such as dating method and first day of last period.
  • 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 due-date and gestational-age estimation only; it excludes ultrasound dating, IVF transfer dating, irregular cycles, 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

Estimate due date as LMP + 280 days plus regular-cycle adjustment, then derive gestational age and trimester from the estimated due date. Key assumptions: This calculator is an educational estimate only and is not medical advice. The estimate assumes an accurately recalled first day of last menstrual period and regular menstrual cycles. Ultrasound dating, IVF transfer dates, irregular cycles, pregnancy complications, and clinician redating are not modeled.

  • Estimate due date as LMP + 280 days plus regular-cycle adjustment, then derive gestational age and trimester from the estimated due date.
  • This calculator is an educational estimate only and is not medical advice.
  • The estimate assumes an accurately recalled first day of last menstrual period and regular menstrual cycles.
  • Primary source context: Merck Manual Professional Edition.

Inputs

Enter first day of last period, regular cycle length, and calculate as of for general wellness education and preparation for a professional conversation. Before calculating, keep units consistent with the labels shown in the form, confirm the date, time, and endpoint convention before comparing results, and stay within the documented minimum and maximum ranges. First day of last period: Use the first day of bleeding from the last menstrual period in YYYY-MM-DD format. Regular cycle length: This estimate assumes regular cycles; irregular cycles need clinician or ultrasound dating. Calculate as of: Used to estimate gestational age and trimester.

First day of last periodUse the first day of bleeding from the last menstrual period in YYYY-MM-DD format.
Regular cycle lengthThis estimate assumes regular cycles; irregular cycles need clinician or ultrasound dating.
Calculate as ofUsed to estimate gestational age and trimester.

Example

Using the default inputs, Pregnancy Calculator returns estimated due date of 2026-10-08. Adjust first day of last period, regular cycle length, and calculate as of to match your own scenario.

FAQ

How is estimated due date calculated here?

Estimate due date as LMP + 280 days plus regular-cycle adjustment, then derive gestational age and trimester from the estimated due date. 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 pregnancy?

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 First day of last period?

Use the first day of bleeding from the last menstrual period in YYYY-MM-DD format. Keep units consistent with the labels shown in the form, confirm the date, time, and endpoint convention before comparing results, and stay within the documented minimum and maximum ranges.

How does Regular cycle length change estimated due date?

This estimate assumes regular cycles; irregular cycles need clinician or ultrasound dating. 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 pregnancy 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 pregnancy 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 formula from LMP, regular-cycle adjustment, and limitations around irregular cycles and ultrasound dating.
    Scope
    Professional medical reference covering gestational age and estimated date of delivery formulas.
    Supports
    EDD formula from LMP, regular-cycle adjustment, and limitations around irregular cycles and ultrasound dating.
    Limits
    Supports educational due-date and gestational-age estimation only; it excludes ultrasound dating, IVF transfer dating, irregular cycles, 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 pregnancy estimate, gestational age weeks/days framing, and first/second/third trimester boundaries.
    Scope
    Consumer medical reference on pregnancy due date, gestational age, and trimester definitions.
    Supports
    280-day pregnancy estimate, gestational age weeks/days framing, and first/second/third trimester boundaries.
    Limits
    Supports educational due-date and gestational-age estimation only; it excludes ultrasound dating, IVF transfer dating, irregular cycles, complications, clinician redating, and clinical scheduling decisions.
  • officialReviewed 2026-05-26 · Source Undated page, accessed 2026-05-26
    PregnancyEunice Kennedy Shriver National Institute of Child Health and Human Development. Pregnancy usually lasting about 40 weeks from the last menstrual period and conservative trimester context.
    Scope
    NIH pregnancy factsheet describing pregnancy duration and trimester framing.
    Supports
    Pregnancy usually lasting about 40 weeks from the last menstrual period and conservative trimester context.
    Limits
    Supports educational due-date and gestational-age estimation only; it excludes ultrasound dating, IVF transfer dating, irregular cycles, 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 due date, gestational age, and clinician review.
    Scope
    Professional guidance on pregnancy due-date estimation and documentation.
    Supports
    Medical limitation context for due date, gestational age, and clinician review.
    Limits
    Does not make this calculator a clinical scheduling or diagnostic tool; ultrasound redating, IVF, complications, and clinician instructions are outside scope.

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.