Compare calculators

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

Ovulation Calculator

Find your estimated ovulation day and 6-day fertile window from how many days ago your last period started, your average cycle length, and your luteal phase. Use it when trying to conceive or to understand your cycle timing.

Days Since Last Period Started (days)

Average Cycle Length (days)

Luteal Phase Length

Number of Cycles to Calculate (cycles)

Fill in the required fields to see your result.

Pregnancy

Baby Size Calculator

Estimates fetal weight and size using gestational age alone or ultrasound measurements (BPD, FL, AC). Used by parents and clinicians to track growth against standard developmental charts.

Gestational Age (weeks)

Additional Days (days) (optional)

Biparietal Diameter (BPD) (mm) (optional)

Femur Length (FL) (mm) (optional)

Abdominal Circumference (AC) (mm) (optional)

Fill in the required fields to see your result.

Key differences

	Ovulation Calculator	Baby Size Calculator
Category	Pregnancy	Pregnancy
Inputs required	4	5
Result	Ovulation & Fertile Window	Estimated Baby Weight (grams)
What it does	Find your estimated ovulation day and 6-day fertile window from how many days ago your last period started, your average cycle length, and your luteal phase. Use it when trying to conceive or to understand your cycle timing.	Estimates fetal weight and size using gestational age alone or ultrasound measurements (BPD, FL, AC). Used by parents and clinicians to track growth against standard developmental charts.