Find how many weeks along you are, your current trimester and your estimated due date.
How this calculator arrives at its answer
Enter the first day of your last period and this calculator estimates how far along the pregnancy is in weeks and days, the current trimester, the due date and days remaining.
It’s an estimate — your provider can confirm dating with an ultrasound.
A worked example
On the values this calculator opens with, the how far along is 17w 1d. Underneath, Trimester comes out at Second and Due date at Jan 18, 2027. Change any field and every figure updates as you type.
Using the calculator
- Enter the first day of your last period.
- Read the weeks along and trimester.
- Note the due date and days remaining.
The formula
weeks along = (today − last period) ÷ 7
due date ≈ last period + 280 days
Common questions
How are pregnancy weeks counted?
From the first day of your last period, so you’re counted as a couple of weeks along before conception — the standard clinical convention.
When do the trimesters change?
Roughly: first trimester through week 12, second through week 26, third from week 27 to birth.
Is the due date exact?
No — it’s an estimate. Most babies arrive within a couple of weeks either side. Confirm with your provider.