How to Calculate Expectation Ranges

Most women, on discovering that they are pregnant, will be keen to know the due date as soon as they can. You can calculate an approximate due date with certain calculations using the date of your last menstrual period as a starting point or, if you know it, the date of conception or date of ovulation. Your doctor will be able to give you a more accurate estimation by also looking at other things, like ultrasound scan results.

Things You'll Need

• Calendar
• Pen
• Paper

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Instructions

• 1

  Add 280 days to the date of the first day of your last period. The average gestation time for humans is 266 days and 14 days is the average amount of time a woman ovulates after the first day of her last period. Therefore, these two figures added together will give you a rough approximation of the due date.

• 2

  Alternatively, add 266 days to the date you last ovulated, if you know it, for a more accurate approximation. Although an average menstrual cycle is 28 days and women usually ovulate halfway through at around 14 days, not everyone is exactly the same. Women trying for a baby often use an ovulation testing kit to determine when they ovulate and, therefore, the best time to conceive. So, if you have a record of your last ovulation date, use that as the basis for your calculations.

• 3

  For the most accurate estimation, add 266 days to the date of conception, if you know it. This would be the most accurate way of estimating your due date.

• 4

  Use an online calculator to determine an estimated due date, if you want to simplify things even further.

• 5

  Add 2 weeks to the estimated due date and take 2 weeks from it to find the expectation range. As Dr. Alison points out on the Health Hype website, "A variation of two weeks either way is considered quite normal and is more often the rule than the exception."