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Both calculators run independently — change the inputs on either side to compare results.

Conception Date Estimate Calculator

Estimate how many days ago conception likely occurred from your last menstrual period, corrected for your cycle length and luteal phase rather than assuming day-14 ovulation.

Days since first day of last period (LMP) (days)

Average menstrual cycle length (days)

Luteal phase length (days)

Days since estimated conception

42 days

Pregnancy

Pregnancy Weeks to Months Converter

Convert pregnancy weeks and days into months and identify your trimester, using either calendar months or four-week 'lunar' months — the two conventions that cause confusion.

Completed weeks of pregnancy (weeks)

Additional days (days)

Month convention

Months and trimester

4.6 months (2nd trimester)

Key differences

	Conception Date Estimate Calculator	Pregnancy Weeks to Months Converter
Category	Pregnancy	Pregnancy
Inputs required	3	3
Result	Days since estimated conception (days)	Months and trimester
What it does	Estimate how many days ago conception likely occurred from your last menstrual period, corrected for your cycle length and luteal phase rather than assuming day-14 ovulation.	Convert pregnancy weeks and days into months and identify your trimester, using either calendar months or four-week 'lunar' months — the two conventions that cause confusion.