What this calculator does
The "How Far Along Am I" calculator tells you how many weeks and days pregnant you are based on your estimated due date (EDD). Doctors and apps usually give you a due date, but you may want to know your exact gestational age at any point in your pregnancy. This tool works backwards from the due date to figure out where you are today.
How to use it
Enter your estimated due date and today's date (it defaults to the current date). The calculator counts the number of days between the two and subtracts that from 280 — the standard length of a full-term pregnancy measured from the first day of your last menstrual period (LMP). The result is shown as completed weeks plus extra days, exactly how clinicians express gestational age (for example, "24 weeks 3 days" or "24w3d").
The formula explained
A pregnancy is conventionally counted as 280 days (40 weeks) from the last menstrual period. If your due date is the 280-day mark, then your current gestational age is simply 280 minus the number of days still remaining until that date:
$$\text{gestationalDays} = 280 - (\text{dueDate} - \text{today})$$
Dividing by 7 gives completed weeks, and the remainder gives the extra days.
Worked example
Suppose your due date is 2024-12-25 and today is 2024-07-03. There are 175 days until the due date. So $$\text{gestationalDays} = 280 - 175 = 105 \text{ days}.$$ Dividing 105 by 7 gives exactly 15 weeks and 0 days. You are 15 weeks pregnant.
FAQ
Is gestational age the same as the baby's age? No. Gestational age is counted from the LMP, which is about two weeks before conception, so it is roughly two weeks more than the actual age of the embryo/fetus.
What if I don't know my due date? You can estimate it by adding 280 days to the first day of your last period, or use an ultrasound-based date from your provider.
Is this medical advice? No. This is an estimate based on the standard 280-day model. Always confirm your dates and progress with your healthcare provider.
