While a missed period and other signs such as morning sickness, smell sensitivity and fatigue are usually indicators of pregnancy, those who are trying to conceive could still be uncertain1.
A pregnancy calculator may be used to accurately gauge if you are indeed pregnant and can estimate how far you’ve come along based on your last menstrual period (LMP)2. This article discusses the function of a pregnancy calculator and how you can be absolutely certain whether you are pregnant.
Expectant mothers may search online for a pregnancy calculator, or download a pregnancy calculator on their mobile devices. To use these digital pregnancy calculators, you have to know the date of the first day of your last menstrual period (LMP), and the average length of your periods.3
Conception occurs when a sperm fertilizes an egg during the ovulation period. Ovulation tends to occur in the four days before or after the midpoint of the menstrual cycle.8 Assuming a regular 28-day cycle, this would be around day 14, or the days immediately before or after.
While conception would not have actually occurred until around the ovulation period, doctors still consider the two or so weeks while your body is preparing for ovulation as part of the pregnancy period.9
A rough way of estimating how many weeks you’ve been pregnant is by taking the date of the first day of your last LMP, considering how many days has passed since then, and dividing it by 7, to determine the number of weeks you’ve been pregnant.5 So if it’s been 28 days since the first day of your last LMP, you can estimate that it might have been 4 weeks since the beginning of your pregnancy period.
It is also important to note that pregnancy calculators using the first day of your last LMP are only applicable to regularly menstruating women or women who have their period every month.4 It is best to think of pregnancy calculators as a guide or an estimation for how long you’ve been pregnant.6
The actual length of pregnancy may also depend on various factors including:3
Age of mother
Length of previous pregnancies
Mother’s birth weight
Using a pregnancy calculator, assumes three things: one, you know when your last menstrual period (LMP) is. Second, you know how long your average cycle length is. And third, your period is regular. While some women keep track of their monthly period information, some women don’t, which makes it difficult for them to remember when their LMP was.
Some women do not have regular menstruation which keeps them from recording their LMP correctly. This is why an ultrasound can find out how far along the expectant mother is in her pregnancy.7 The doctor will perform an ultrasound scan to look at the various growth parameters of the fetus before determining how many weeks of gestation the fetus corresponds to. Thus, always refer to the doctor for a more accurate understanding of your pregnancy journey.
It is helpful to have an idea of how many weeks you’ve been pregnant so you can make plans based on how far you’ve come along. You can use this information to determine when you can file for maternity leave, and when to start making practice runs to the hospital. This information will also help your doctor determine what your needs are during a particular phase of pregnancy.
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1. Early Pregnancy Symptoms (September 5, 2018). Retrieved September 3, 2020 from:
2. Calculating a Due Date. Retrieved September 3,, 2020 from:
3. Pregnancy Calculator (n.d.). Retrieved July 31, 2020 from:
4. How Many Weeks Pregnant Am I? – Pregnancy Calculator (n.d.). Retrieved July 31, 2020 from:
5. How far along am I? Four ways to figure out how pregnant you are (June 14, 2019). Retrieved July 31, 2020 from:
6. Do Pregnancy Calculators Work? (January 22 , 2018). Retrieved July 31, 2020 from:
7. Ultrasound Scans In Pregnancy (2020). Retrieved July 17, 2020 from:
8. What ovulation signs can I look out for if I'm hoping to conceive? (August 16, 2019). Retrieved July 31, 2020 from:
9. You and your pregnancy at 1 to 3 weeks (Last reviewed July 17, 2018). Retrieved July 31, 2020 from: