In pregnancy due date calculation, which formula is shown?

In pregnancy due date calculation, which formula is shown?

• A. LMP + 7 days - 3 months + 1 year
• B. LMP + 28 days
• C. LMP + 9 months
• D. Add 40 weeks to the LMP

Answer: (A)

The main idea is that due dates are estimated from the last menstrual period using a standard rule. Take the first day of the LMP, add seven days, subtract three months, and add one year. This sequence yields a date about 40 weeks after the LMP, which is the typical length of pregnancy used for estimating due dates. The reason this rule is reliable is that it accounts for the average gestation and handles month boundaries cleanly, giving a calendar-consistent due date. Adding 28 days assumes a fixed 28-day cycle and isn’t accurate for most people. Adding 9 months omits the extra 7 days that push the date into the next week or month. Adding 40 weeks to the LMP is a common shorthand, but the precise, widely used calculation is the LMP plus 7 days, minus 3 months, plus 1 year.

The main idea is that due dates are estimated from the last menstrual period using a standard rule. Take the first day of the LMP, add seven days, subtract three months, and add one year. This sequence yields a date about 40 weeks after the LMP, which is the typical length of pregnancy used for estimating due dates. The reason this rule is reliable is that it accounts for the average gestation and handles month boundaries cleanly, giving a calendar-consistent due date.

Adding 28 days assumes a fixed 28-day cycle and isn’t accurate for most people. Adding 9 months omits the extra 7 days that push the date into the next week or month. Adding 40 weeks to the LMP is a common shorthand, but the precise, widely used calculation is the LMP plus 7 days, minus 3 months, plus 1 year.