BabyMakers

Pregnancy test calculator: when to test in the two-week wait

This pregnancy test calculator works out the dates of your two-week wait, the days between ovulation and your expected period: when implantation is likely, when your period is due, and the earliest day a home pregnancy test gives a reliable result.

Calculate from

From an ovulation predictor kit, basal body temperature charting or a scan.

From the first day of one period to the day before the next.

Optional details

The days from ovulation to your next period. Leave it at 14 unless you have measured your own.

Seek help now if you have any of these symptoms

Bleeding and cramping are common in early pregnancy and often do not mean miscarriage. The symptoms below, however, need to be assessed straight away.

  • Soaking two or more sanitary pads per hour, or passing large clots
  • Severe lower abdominal pain, especially on one side
  • Pain at the tip of the shoulder
  • Dizziness, fainting, or collapse
  • Signs of shock — pale, clammy, rapid heartbeat, breathlessness
  • Pain on opening bowels, or bladder or bowel changes
  • Feeling very unwell, or feverish
Emergency911
Urgent adviceyour OB provider, or labor and delivery triageNo universal nurse line. OB provider or L&D triage.
ThenOB office, or nearest ER / L&D triage.

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How this is calculated

Implantation window = ovulation + 6 to 12 days

Period due = ovulation + luteal phase length

Reliable test from = ovulation + 14 days, or the day the period is due if that is later

Ovulation, from a last period = first day of last period + (cycle length − luteal phase length)

In a study of 221 women trying to conceive, hCG first appeared in urine 6 to 12 days after ovulation in pregnancies that continued, and on day 8, 9 or 10 in about 80 in 100 of them. A home test detects a pregnancy only once hCG has risen to a level the test can measure.

The NHS advises that pregnancy tests are most reliable from the first day of a missed period, and that a negative result is less reliable than a positive one.

Sources: Wilcox, Baird and Weinberg, Time of implantation of the conceptus and loss of pregnancy (New England Journal of Medicine, 1999; 221 women); NHS, Doing a pregnancy test; ASRM Practice Committee, Diagnosis and treatment of luteal phase deficiency: a committee opinion (Fertility and Sterility, 2021).

A pregnancy test cannot detect a pregnancy before implantation

Home pregnancy tests detect human chorionic gonadotropin (hCG), a hormone that appears once the embryo has implanted in the lining of the uterus; the NHS puts the start of hCG production at around 6 days after fertilization (NHS). In a study of 221 women trying to conceive, hCG first appeared in urine between 6 and 12 days after ovulation in pregnancies that continued, and on day 8, 9 or 10 in 84 in 100 of them (Wilcox, Baird and Weinberg, New England Journal of Medicine, 1999). The implantation window the calculator shows is that range.

An early negative result is not conclusive

A test taken before hCG has risen far enough reads negative even when a pregnancy has begun. That is a false negative, and it is the reason the calculator gives the earliest date a result is reliable, not the earliest date a test might turn positive. The NHS says that a positive result is almost certainly correct, that a negative result is less reliable, and that a test is most reliable from the first day of a missed period (NHS, Doing a pregnancy test).

Days past ovulation (DPO) count from the day of ovulation

The day of ovulation is 0 DPO and the day after it is 1 DPO. When you enter an ovulation date or a last period, the calculator shows today's DPO beside the implantation window and the date your period is due.

Some symptoms after a positive test need checking straight away

The section above lists the symptoms that need checking straight away after a positive test, and who to contact where you are. In the UK, the NHS advises calling 999 or going to A&E immediately if you are pregnant and bleeding with severe tummy pain, shoulder pain, feeling sick, faint or dizzy, or heavy bleeding that soaks a period pad soon after you put it on (NHS, Vaginal bleeding in pregnancy). It also advises contacting your GP or NHS 111 if you have a combination of symptoms such as vaginal bleeding, tummy pain low down on one side and shoulder tip pain and think you might be pregnant, even before a positive test (NHS, Ectopic pregnancy: symptoms).

Sources

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