Trimester Calculator (Exact Dates)
Your personal first/second/third trimester boundary dates from LMP or EDD.
ACOG retired plain 'term' in 2013: 37–38w6d is now *early* term, 39–40w6d *full* term — outcomes measurably differ, which is why elective deliveries wait for 39 weeks. Different books draw the trimester lines a week or two apart; the 13/28 convention here is the most widely used clinically.
Formula
For general information only. Pregnancy and infant care decisions must be guided by your treating clinician or midwife — always defer to their assessment.
Your personal first/second/third trimester boundary dates from LMP or EDD. The Trimester Calculator (Exact Dates) is a free, private trimester calculator tool — every result computes instantly in your browser with no sign-up and no data upload.
About Trimester Calculator (Exact Dates)
ACOG retired plain 'term' in 2013: 37–38w6d is now *early* term, 39–40w6d *full* term — outcomes measurably differ, which is why elective deliveries wait for 39 weeks. It applies boundaries at 13w0d and 28w0d from LMP; 'full term' = 39w0d–40w6d. Use the Trimester Calculator (Exact Dates) to get an instant, clearly-explained result with the working shown step by step — free, private and with the source method cited.
How to use Trimester Calculator (Exact Dates)
- 1Enter your details in the Trimester Calculator (Exact Dates) input fields above.
- 2The result updates instantly with the working and reference bands shown.
- 3Adjust any value to explore how it changes the outcome — it's free and unlimited.
Why use Trimester Calculator (Exact Dates)?
- ✓Instant trimester calculator result that recomputes as you type — no waiting, no page reloads
- ✓100% client-side: your health data never leaves your browser
- ✓Shows the actual formula and your numbers substituted in, so you can see exactly how the result is reached
- ✓Based on published, citable sources (ACOG Committee Opinion 579 — definition of term pregnancy)
- ✓Free forever with no sign-up, account or app install
Frequently asked questions
How does the Trimester Calculator (Exact Dates) work?+
ACOG retired plain 'term' in 2013: 37–38w6d is now *early* term, 39–40w6d *full* term — outcomes measurably differ, which is why elective deliveries wait for 39 weeks. The calculation uses the formula: boundaries at 13w0d and 28w0d from LMP; 'full term' = 39w0d–40w6d. Everything runs instantly in your browser as you type — your inputs are never uploaded.
Is the Trimester Calculator (Exact Dates) accurate, and what is it based on?+
The method is traceable to authoritative sources: ACOG Committee Opinion 579 — definition of term pregnancy. Results are estimates — individual variation always applies, so treat the output as a well-grounded starting point.
Is the Trimester Calculator (Exact Dates) free and private?+
Yes. It's completely free with no sign-up, and all computation happens locally in your browser, so none of your health data ever leaves your device.
Can I use this for medical decisions?+
This tool is informational only. Always defer to your treating clinician or midwife for pregnancy and infant care decisions.
What can I use the Trimester Calculator (Exact Dates) for?+
It's commonly used for trimester calculator, trimester dates, when does second trimester start. Your personal first/second/third trimester boundary dates from LMP or EDD.
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