About

Standard pregnancy calculators rely heavily on the Last Menstrual Period (LMP). However, women with irregular cycles or those tracking basal body temperature often know their exact Ovulation Date. This precise data point allows for a more accurate calculation of gestational age, bypassing the assumption of a Day 14 ovulation. This tool provides two distinct modes: one for planning conception and one for tracking progress once confirmed.

In the "Expectant" mode, the calculator standardizes the biological timeline. Since clinical pregnancy dating conventionally includes the two weeks prior to ovulation, this tool adds 14 days to the time elapsed since ovulation to align with medical standards (LMP-equivalent dating). This ensures compatibility with doctor's charts while utilizing the superior accuracy of the ovulation date.

Formulas

For users in the "Expectant" phase, the gestational age GA is calculated by referencing the known Ovulation Date D_ov against the Current Date D_now and adding the clinical standard offset.

GA_days = (D_now − D_ov) + 14

This result is then converted into weeks and days:

Weeks = floor(GA_days7)

Reference Data

Gestational Week	Developmental Stage	Fetus Size Analogy	Avg Length (Crown-Rump)
Week 4	Implantation	Poppy Seed	1 mm
Week 8	Organogenesis	Raspberry	16 mm
Week 12	Reflexes Develop	Plum	5.4 cm
Week 16	Muscular Activity	Avocado	11.6 cm
Week 20	Vernix Caseosa	Banana	25.6 cm
Week 24	Viability Milestone	Ear of Corn	30 cm
Week 28	Eyes Open	Eggplant	37.6 cm
Week 32	Rapid Weight Gain	Napa Cabbage	42.4 cm
Week 36	Lungs Mature	Papaya	47.4 cm
Week 40	Full Term	Watermelon	51.2 cm

Frequently Asked Questions

Medical pregnancy dating traditionally starts from the first day of the Last Menstrual Period (LMP), roughly 14 days before ovulation in a standard cycle. To align your precise ovulation data with doctor's records and due date standards, we add these 14 "phantom" days back into the calculation.

Yes, specifically for women with irregular cycles. If you ovulated on day 20 of your cycle instead of day 14, an LMP calculator would overestimate your pregnancy progress by nearly a week. Using the ovulation date removes this variable, providing the true biological age of the fetus.

The size comparisons are averages based on standard growth charts. Individual fetal growth rates vary, especially in the third trimester. Early pregnancy measurements (Crown-Rump Length) are generally consistent across populations.

Absolutely. For IVF, treat the date of retrieval (or fertilization) as the "Ovulation Date". If you had a 3-day transfer, subtract 3 days from the transfer date to get the theoretical ovulation date. For a 5-day transfer, subtract 5 days.