❤️HealthUpdated March 2026

Free Pregnancy Due Date Calculator 2026 — Estimate Your Due Date

Calculate your estimated due date from LMP, estimated conception date, or ultrasound results. See your current gestational age and trimester. Free and instant.

All calculations are estimates. Only your healthcare provider can confirm your due date.

How to use this calculator

  1. 1Select your calculation method: Last Period (LMP), Conception Date, or Ultrasound.
  2. 2Enter the relevant date (last period start, conception date, or ultrasound date).
  3. 3For the ultrasound method, also enter how many weeks you were at the scan.
  4. 4View your estimated due date, current gestational age, and trimester.

Written by FreeToolCalc Team

Formulas based on standard financial/medical equations. Last updated: March 2026.

How Pregnancy Due Dates Are Calculated

A pregnancy due date is one of the first and most important pieces of information your healthcare provider will determine. It guides all subsequent prenatal care, ultrasound timing, and delivery planning. Our calculator uses the same three methods OBs use: last menstrual period (LMP), conception date, and ultrasound dating.

Naegele's Rule — The Standard LMP Calculation

// Naegele's Rule
Due Date = LMP First Day + 280 days (40 weeks)
// Conception-based
Due Date = Conception Date + 266 days (38 weeks)

Pregnancy Week by Week Milestones

WeekTrimesterKey Development
Week 41stPositive pregnancy test possible
Week 61stHeartbeat detectable on ultrasound
Week 101stAll major organs have formed
Week 121stEnd of highest-risk period; NT scan
Week 16–202ndMovement felt (quickening); anatomy scan
Week 242ndViability milestone (intensive care survival)
Week 283rdBegins 3rd trimester
Week 373rdEarly term (safe for birth)
Week 39–403rdFull term — optimal for most births
Week 423rdPost-term; induction typically recommended

Prenatal Visit Schedule

  • Weeks 4–28: Monthly visits (approximately every 4 weeks)
  • Weeks 28–36: Every 2 weeks
  • Weeks 36–40+: Weekly until delivery

Important: This calculator is for informational and planning purposes only. Only your licensed obstetrician or midwife can confirm your pregnancy due date through clinical assessment and ultrasound. Seek prenatal care as early as possible after a positive pregnancy test.

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Frequently Asked Questions

How is a due date calculated from the last period?

Naegele's Rule: Add 280 days (40 weeks) to the first day of your last menstrual period. This assumes a 28-day cycle with ovulation on day 14. Due date = LMP date + 280 days. Alternatively: LMP + 9 months + 7 days. For cycles not 28 days, your OB will adjust accordingly.

How accurate is the estimated due date?

Only about 5% of babies are born on their exact due date. A full-term pregnancy is 37–42 weeks. The due date is an estimate based on an average 40-week pregnancy. Early ultrasound (before 13 weeks) is the most accurate method for dating — typically within ±5 days of the actual delivery date.

What are the pregnancy trimesters?

First Trimester: Weeks 1–12 (conception through end of week 12). Second Trimester: Weeks 13–26 — often called the 'golden trimester' as morning sickness typically fades. Third Trimester: Weeks 27–40+ — baby gains most weight and prepares for birth.

What does gestational age mean?

Gestational age measures pregnancy from the first day of the last menstrual period — not conception. So at the moment of fertilization, you're already considered '2 weeks pregnant' by gestational age. A full-term pregnancy is 40 weeks gestational age (38 weeks from actual conception).

When should I have my first prenatal appointment?

Most OBs recommend scheduling your first prenatal visit at 8–10 weeks after your last period. Some practices see patients as early as 6–8 weeks for confirmation and early ultrasound. Call to schedule as soon as you have a positive pregnancy test.