Pregnancy Calculator

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Estimated pregnancy dating timeline

Pregnancy Calculator for Due Date and Gestational Age

Estimate an expected due date and pregnancy timeline from the first day of the last menstrual period, conception date, a known due date, IVF transfer or ultrasound dating. The calculation exposes every day adjustment and lets you choose the as-of date used for gestational age.

Pregnancy dating inputs

Estimated pregnancy schedule

Pregnancy due-date and gestational-age guide

This pregnancy calculator provides a dedicated calculation workflow rather than a generic converter. Pregnancy dates are estimates. Clinical dating may prioritize an early ultrasound or other medical information when it differs from calendar-based calculation.

Dating from the last menstrual period

The standard LMP estimate adds 280 days to the first day of the last menstrual period. The calculator also adjusts by cycle length relative to a 28-day cycle.

Dating from conception or IVF

Conception dating adds 266 days. For IVF, embryo age is already known, so a day-3 transfer adds 263 days and a day-5 transfer adds 261 days to the transfer date.

Dating from ultrasound

Enter the date of the scan and the gestational weeks and days assigned at that scan. The calculator adds the remaining days required to reach 40 weeks.

Gestational age on a chosen date

Gestational age is measured from the calculated gestational start, about two weeks before conception in standard dating. The result reports completed weeks and remaining days.

Milestones are planning dates

The timeline includes common week markers such as 12, 20, 28, 37 and 40 weeks. Appointments, screening windows and clinical decisions must follow the treating professional’s plan.

Is the due date the predicted birth date?

No. It is an estimated 40-week reference date, and birth can occur before or after it.

Why does LMP dating begin before conception?

Gestational age conventionally starts from the last menstrual period, usually about two weeks before ovulation and conception.

Can this replace ultrasound dating?

No. A clinician may revise dates using ultrasound and the full clinical history.

Pregnancy Calculator: formula-based step-by-step solution

This Pregnancy Calculator worked derivation uses the published default state. Its live formula panel replaces these values whenever an input, unit, mode, date, material, or scenario changes.

Governing formula or algorithm — exact production relationships:
  1. Ref = parseDate(Date,'Reference date')
  2. As Of = parseDate(As Of,'As-of date')
  3. Conception = add(start,14)
  4. Gest Days = floor((asOf-start) ÷ DAY)
  5. Weeks = gestDays>=0?floor(gestDays ÷ 7):ceil(gestDays ÷ 7)
  6. Days = gestDays>=0?gestDays%7:|gestDays%7|
  7. Days To Due = ceil((due-asOf) ÷ DAY)
  8. Term Start = add(start,259)

1. Governing formulas and numeric substitution

  1. Formula 1: Ref = parseDate(Date,'Reference date')
    Default-value substitution: Ref = parseDate(Date,'Reference date') | current data: Calculate from=lmp; Reference date=2026-04-15; Average cycle length (days)=28 days; Gestational weeks at ultrasound=12; Additional days at ultrasound=3; Calculate gestational age on=2026-07-29
  2. Formula 2: As Of = parseDate(As Of,'As-of date')
    Default-value substitution: As Of = parseDate(As Of,'As-of date') | current data: Calculate from=lmp; Reference date=2026-04-15; Average cycle length (days)=28 days; Gestational weeks at ultrasound=12; Additional days at ultrasound=3; Calculate gestational age on=2026-07-29
  3. Formula 3: Conception = add(start,14)
    Default-value substitution: Conception = add(start,14) | current data: Calculate from=lmp; Reference date=2026-04-15; Average cycle length (days)=28 days; Gestational weeks at ultrasound=12; Additional days at ultrasound=3; Calculate gestational age on=2026-07-29
  4. Formula 4: Gest Days = floor((asOf-start) ÷ DAY)
    Default-value substitution: Gest Days = floor((asOf-start) ÷ DAY) | current data: Calculate from=lmp; Reference date=2026-04-15; Average cycle length (days)=28 days; Gestational weeks at ultrasound=12; Additional days at ultrasound=3; Calculate gestational age on=2026-07-29
  5. Formula 5: Weeks = gestDays>=0?floor(gestDays ÷ 7):ceil(gestDays ÷ 7)
    Default-value substitution: Weeks = gestDays>=0?floor(gestDays ÷ 7):ceil(gestDays ÷ 7) | current data: Calculate from=lmp; Reference date=2026-04-15; Average cycle length (days)=28 days; Gestational weeks at ultrasound=12; Additional days at ultrasound=3; Calculate gestational age on=2026-07-29
  6. Formula 6: Days = gestDays>=0?gestDays%7:|gestDays%7|
    Default-value substitution: Days = gestDays>=0?gestDays%7:|gestDays%7| | current data: Calculate from=lmp; Reference date=2026-04-15; Average cycle length (days)=28 days; Gestational weeks at ultrasound=12; Additional days at ultrasound=3; Calculate gestational age on=2026-07-29
  7. Formula 7: Days To Due = ceil((due-asOf) ÷ DAY)
    Default-value substitution: Days To Due = ceil((due-asOf) ÷ DAY) | current data: Calculate from=lmp; Reference date=2026-04-15; Average cycle length (days)=28 days; Gestational weeks at ultrasound=12; Additional days at ultrasound=3; Calculate gestational age on=2026-07-29
  8. Formula 8: Term Start = add(start,259)
    Default-value substitution: Term Start = add(start,259) | current data: Calculate from=lmp; Reference date=2026-04-15; Average cycle length (days)=28 days; Gestational weeks at ultrasound=12; Additional days at ultrasound=3; Calculate gestational age on=2026-07-29

2. Variables and measurement units used

  1. Calculate from = lmp
  2. Reference date = 2026-04-15
  3. Average cycle length (days) = 28 days
  4. Gestational weeks at ultrasound = 12
  5. Additional days at ultrasound = 3
  6. Calculate gestational age on = 2026-07-29

3. Pregnancy Calculator final evaluation: this calculator’s production engine evaluates the substituted relationship with unrounded internal precision; its subject-specific result cards, table, and visual report the rounded final answer and verification quantities.

Formula-based calculator guide

Pregnancy Calculator: formula, steps, units and verification

pregnancy calculator is designed for a transparent calculation rather than a black-box answer. Pregnancy Calculator: calculate pregnancy with task-specific inputs, transparent formulas, intermediate steps, unit checks, validation and responsive results.

How to use the pregnancy calculator in 5 steps

  1. Choose the required mode. Select the calculation path that matches the quantity you know and the result you need.
  2. Enter source values. Use measured, documented or assignment values rather than rounded estimates whenever possible.
  3. Confirm every unit. The pregnancy calculator converts supported units before formula substitution, so each selector must describe the entered number.
  4. Run the calculation. Review the displayed formula, normalized values and numeric substitution before accepting the final result.
  5. Verify the answer. Reproduce the substitution manually and check whether the output is reasonable for the stated assumptions.

Pregnancy Calculator formula and unit checks

The pregnancy calculator keeps source inputs, canonical calculation units and displayed output units separate. This prevents a correct formula from producing a wrong answer because feet were treated as meters, percentages as decimals, or time values as the wrong interval.

For an independent check, copy the formula shown by the calculator, substitute the unrounded canonical values, preserve full precision through intermediate operations and round only the final result. The verified answer should match both the displayed number and its measurement unit.

How to interpret the pregnancy calculator result

A result is useful only when its assumptions match the real problem. Compare the answer with expected ranges, inspect any warning or boundary message, and test a nearby input to confirm that the output changes in the direction predicted by the governing relationship.

The pregnancy calculator provides an educational and planning result. For regulated, medical, structural, financial, laboratory or safety-critical decisions, verify the inputs and method against the applicable professional requirements before acting.

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Pregnancy Calculator quick verification checklist

Before saving or reporting a result from the pregnancy calculator, confirm the input source, unit selections, formula mode, intermediate substitution, final unit and rounding rule. These checks make the calculation reproducible and easier to audit.

Browse the complete published calculator sitemap or return to the Salar Cafe home page.

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