Due Date Calculator

Understand due dates and pregnancy timelines

Why due dates are estimates

EDD is a projection, not a promise. It assumes a 40‑week pregnancy counted from LMP. Individual ovulation timing, cycle length, and early fetal measurements can shift the estimate. Many healthy babies arrive before or after the EDD.

Methods to calculate EDD

• LMP method: Add 280 days (40 weeks) to the first day of your last menstrual period. If your cycle isn’t 28 days, adjust by the difference.
• Conception/ovulation date: Add 266 days (38 weeks) to conception; this counts pregnancy from fertilization.
• Ultrasound dating: Early scans (especially first trimester) provide strong estimates. Enter the scan date and weeks+days to project EDD.
• IVF transfer: Use standard offsets from transfer date (e.g., Day‑3 +261 days; Day‑5 +259 days).

Trimesters and milestones

• Trimester 1 0–13w6d: Foundation stage; organ formation and early development.
• Trimester 2 14–27w6d: Growth spurt; anatomy scan and quickening for many.
• Trimester 3 28–40w: Rapid growth and maturation; prepare for birth.

Cycle length and adjustments

If your average cycle is longer or shorter than 28 days, LMP‑based EDD can be shifted by that difference. Longer cycles often ovulate later; shorter cycles earlier. Ultrasound is the most practical way to reconcile differences.

Practical tips

• Track key dates: LMP, positive test, and early ultrasounds help refine EDD.
• Expect a range: Focus on weeks, not a single day; plan flexibility around the EDD.
• Use milestones: Plan screenings and checkups with trimester boundaries in mind.

Safety and limitations

This tool is for education and global use. If your official EDD from your clinician differs from the calculator, follow clinical guidance. For urgent concerns, seek local care.

Frequently asked questions

• HOW TO calculate due date from LMP? Add 280 days (40 weeks) to the first day of your last menstrual period. Adjust if your cycle isn’t 28 days.
• HOW TO find EDD from conception? Add 266 days (38 weeks) to the conception or ovulation date.
• HOW TO use ultrasound weeks and days? Enter the scan date and the gestational age. The calculator projects your EDD and trimester dates.
• HOW TO calculate IVF due date? Use transfer date offsets: Day‑3 embryo +261 days; Day‑5 blastocyst +259 days.
• HOW TO interpret trimesters? T1: 0–13w6d (98 days), T2: 14–27w6d (98 days), T3: 28–40w (84 days). The chart shows their relative durations.