What is the Weeks Pregnant from Conception Calculator?
This calculator estimates your gestational age — how many weeks pregnant you are — using the date conception likely occurred. Clinically, pregnancy is dated from the first day of the last menstrual period (LMP), which is about two weeks before conception. So if you know the conception date, you add roughly two weeks to convert "weeks since conception" into the standard gestational age that doctors and ultrasounds use.
How to use it
Enter the date of conception (or your estimated ovulation date) and today's date. The tool counts the days between them, divides by 7 to get weeks since conception, then adds 2 weeks to express the result as gestational age. It also shows the answer broken down into whole weeks and remaining days, the format midwives commonly use (e.g. "12w 3d").
The formula explained
The core equation is:
$$\text{Gestational Weeks} = \frac{\text{Today} - \text{Conception Date}}{7} + 2$$
The division by 7 converts elapsed days into weeks. The "+2" accounts for the standard convention that gestational age begins at the LMP, approximately 14 days before conception.
Worked example
Suppose conception occurred on 2024-01-01 and today is 2024-02-12. That is 42 days. \(42 \div 7 = 6\) weeks since conception. Adding 2 gives a gestational age of 8.0 weeks — exactly 8 weeks and 0 days pregnant.
FAQ
Is this the same as my due date estimate? It estimates current gestational age; a due date is 40 weeks from the LMP, or about 38 weeks from conception.
Why add two weeks? Because conventional pregnancy dating starts at the last period, which precedes conception by roughly 14 days.
How accurate is it? It is an estimate. Conception and ovulation timing vary, so an early ultrasound remains the most reliable dating method.
