Pregnancy Due Date Calculator
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First trimester

1 weeks pregnant

At 1 week, you are not pregnant yet. Pregnancy is counted from the first day of your last period, about two weeks before conception usually happens, so the first two weeks are your body getting ready for a possible pregnancy.

This page covers 1 weeks 0 days to 1 weeks 6 days (1+0 to 1+6), counted from the first day of the last period. Check how far along you are

Enter it to see the calendar dates of your week 1.

Pregnancy weeks start before conception, so there is no embryo to measure yet.

What is happening in your body

  • There is no embryo yet. Gestational age is measured from the first day of your last period because the exact day of conception usually can't be known, so weeks 1 and 2 happen before you are pregnant.1,2
  • This way of counting puts the start of pregnancy about two weeks ahead of when conception actually occurs. It's why your provider asks for the date your last period started.3
  • During these first two weeks, hormones prepare your body for a possible pregnancy. An egg develops in one of your ovaries, and the lining of your womb starts to thicken.3,4
  • Your estimated due date is worked out by adding 280 days (40 weeks) to the first day of your last period.5

Changes you may notice

Everyone’s experience is different. You may notice some of these, or none.

  • The first day of your period is day 1 of your menstrual cycle, and the start of week 1 of a pregnancy count. Periods usually last around 2 to 7 days.4
  • Cycle length varies from person to person. Regular cycles anywhere from 21 to 35 days are normal, so the timing of ovulation, and of conception, differs too.4
  • In each cycle, rising estrogen helps an egg develop in the ovary and the womb lining begins to build up. You won't notice any pregnancy symptoms at this stage.4

Care around this week

  • If you could become pregnant, a daily folic acid supplement is recommended before pregnancy. The CDC advises 400 micrograms a day, starting at least 1 month before conception. The NHS suggests 400 micrograms a day, ideally starting 3 months before, and continuing for the first 12 weeks.6,7
  • Neural tube defects develop in the first few weeks of pregnancy, often before people know they are pregnant. That is why folic acid is recommended before conception.6
  • Other preconception steps often recommended: get support to stop smoking, avoid alcohol and illegal drugs, check your vaccinations such as MMR, and get tested for STIs if needed. Don't stop a prescribed medicine without first talking to your doctor or specialist.8

Questions to ask your provider

  • Should I start taking folic acid now, and is the standard dose right for me?
  • Do any of my current medicines need reviewing before I try to get pregnant?
  • Are my vaccinations, such as MMR, up to date?
  • Is there anything about my health conditions I should plan for before pregnancy?

Questions about 1 weeks

Am I pregnant at 1 week?

No. Pregnancy is dated from the first day of your last period, so during weeks 1 and 2 you are not yet pregnant. Your body is preparing for a possible pregnancy.1,2

Why is pregnancy counted from my last period instead of conception?

The exact day of conception usually isn't known, but the first day of your last period is a date most people can recall. Gestational age is measured from that date, which is about two weeks before conception.1,3

How is my due date calculated?

The standard estimate adds 280 days to the first day of your last period. An early ultrasound, done up to 13 weeks 6 days, gives the most accurate dating.5

Sources

  1. Fetal developmentUS National Library of Medicine
  2. How Your Fetus Grows During PregnancyAmerican College of Obstetricians and Gynecologists
  3. Fetal development: week-by-week stages of pregnancyCleveland Clinic
  4. Periods and fertility in the menstrual cycleNHS (England)
  5. Committee Opinion No. 700: Methods for Estimating the Due DateAmerican College of Obstetricians and Gynecologists, with AIUM and SMFM, 2017
  6. About folic acidUS Centers for Disease Control and Prevention
  7. Pregnancy vitamins and supplementsNHS (England)
  8. Trying to get pregnantNHS (England)

Links checked November 12, 2026. Citing a source does not mean it endorses this site.

Written from the sources above and checked against them on 2026-11-12. Not reviewed by a clinician. Our editorial policy