Calculating your time of pregnancy is important regardless if you decide to terminate or continue the pregnancy.
If you decide to end the pregnancy, the weeks of gestation will help determine which options of abortion methods are available for you.
If you decide to continue the pregnancy, this will help your midwife or doctor know if the pregnancy is evolving normally. Keep in mind that a pregnancy usually lasts around 38 to 42 weeks from the first day of your last menstrual period. 
The easiest way to calculate the weeks of your pregnancy is by counting the number of weeks and days from the first day of your last menstrual period.
It is important to count from the first day of your most recent menstrual period , because from this we can estimate when the egg was released and fertilized. 
Be careful with some of the common mistakes, do NOT calculate by:
- counting from when you missed your period;
- counting from the day of sexual intercourse;
- counting from the day you think you became pregnant.
If you need help calculating the weeks of your pregnancy, select the first day of your last menstrual period here.
If you do not keep track of your period or you cannot remember the last time you had it, think back to what you were doing when you last got it. Where were you? Who were you with? This sometimes helps you remember the date when your last period occurred. 
Other ways to confirm pregnancy include:
1) Urine test: This test is very common, and it detects the presence of pregnancy hormone in the urine. In order to avoid a "false negative" this test should be done 2 weeks or more after unprotected sex.
- Benefits: It is inexpensive and can be done privately at home.
- Disadvantages: It does not help calculate the age of the pregnancy.
2) Blood test: Two types of this blood test exist: qualitative (detects the pregnancy hormone hCG in the blood) and quantitative (measures the amount of hormone).
- Benefits: It can detect earlier pregnancy than the urine test, and can sometimes help determine the approximate age of the pregnancy (if quantitative).
- Disadvantages: It is more expensive, and must be ordered by a health provider.
3) Ultrasound: This test is useful after at least 4 weeks of pregnancy or more, otherwise nothing will be seen. It can be particularly helpful if you do not know your last menstrual period.
- Benefits: It is very accurate to estimate the gestational age, and can also be used to identify ectopic pregnancy or other non-viable pregnancy.
- Disadvantages: It can be very expensive, and must be performed by a health provider. 
 World Health Organization. Safe abortion: technical and policy guidance for health systems. Retrieved from: https://apps.who.int/iris/bitstream/handle/10665/70914/;jsessionid=B7AEEBE4F34809D869F73B1ABA7F6221?sequence=1
 Megan Wainwright, Christopher J Colvin, Alison Swartz & Natalie Leon. Self-management of medical abortion: a qualitative evidence synthesis. Retrieved from: https://www.tandfonline.com/doi/pdf/10.1016/j.rhm.2016.06.008?needAccess=true
 WebMd. Pregnancy Tests. Retrieved from: https://www.webmd.com/baby/guide/pregnancy-tests#1