Trimester Calculator

Free pregnancy trimester calculator. Find which trimester you're in and when each begins. Track your pregnancy journey by trimester.

Determine which trimester of pregnancy you're in and when each trimester begins and ends. Enter your due date or last period date to see your pregnancy timeline broken into trimesters.

Common use cases

  • Expectant parents tracking pregnancy stages
  • Understanding fetal development phases
  • Planning by trimester milestones
  • Communicating pregnancy progress
  • Scheduling trimester-specific care

How to use

  1. Enter your due date or last period date
  2. View your current trimester
  3. See start and end dates for each trimester
  4. Track how many weeks into your trimester
  5. View key milestones for each stage

FAQ

When does each trimester start?

First: weeks 1-12. Second: weeks 13-27. Third: weeks 28 until delivery (around week 40).

Why are trimesters important?

Each trimester has different developmental milestones, risks, and care recommendations.

How is this different from months?

Trimesters divide the ~40-week pregnancy into three roughly equal phases; months don't align as cleanly with pregnancy stages.