acalculator

When should I take a pregnancy test?

Enter the first day of your last period, your ovulation day, or the day you had sex to see when to take a home pregnancy test.

Your numbers

What do you know?
Test on or after
October 6, 2026

Take a home pregnancy test on or after October 6, 2026.

More reliable from
October 13, 2026
Expected period
October 6, 2026
Ovulation
September 22, 2026
Implantation from
September 28, 2026
Implantation up to
October 4, 2026

Answer for the example date Tuesday, September 29, 2026. It changes to today's date when the page loads.

Test on or after: October 6, 2026. Take a home pregnancy test on or after October 6, 2026.

What happens between ovulation and the test?

This calculator gives general information only. It is not medical advice and does not replace a doctor or other health care provider. Talk with a professional about your results. Terms of use

How to calculate

Works out when to take a home pregnancy test: from the first day of the missed period (from the last period or the ovulation date), or 21 days after sex, with the likely implantation window.

Example with the default inputs (What do you know? Last period, First day of your last period September 8, 2026, Cycle length (days) 28) on the example date Tuesday, September 29, 2026: Take a home pregnancy test on or after October 6, 2026.

Method: Expected period = last period + cycle length (or ovulation + 14 days); test on the expected period, more reliably 7 days later; implantation 6 to 12 days after ovulation. From a day of sex: test 21 days later.

  • Ovulation comes 14 days before the expected period (ACOG average); real cycles vary.
  • A test cannot be positive before implantation, which is usually 6 to 12 days after ovulation, most often 8 to 10 (Wilcox and others, 1999).
  • Even with a very sensitive test, about 10% of pregnancies are not yet detectable on the first day of the missed period; 1 week later, at most 3% are not (Wilcox and others, 2001).
  • Home tests differ in sensitivity. Follow the instructions on your test, and see a health care professional for a blood test or advice. This is not medical advice.

Machine-readable copies: Markdown, JSON.

Worked examples

Each example is checked against the calculator on every build.

  1. What do you know? Last period, First day of your last period 2026-09-01, Cycle length (days) 28 gives Test on or after 2026-09-29, More reliable from 2026-10-06, Expected period 2026-09-29, Ovulation 2026-09-15, Implantation from 2026-09-21, Implantation up to 2026-09-27.Source: hand calculation in content.mdx: ACOG (28-day cycle, ovulation 14 days before the period); NHS (test from the first day of a missed period); Wilcox 1999 (implantation 6 to 12 days after ovulation); Wilcox 2001 (1 week later)
  2. What do you know? Ovulation day, Ovulation day 2026-10-10 gives Test on or after 2026-10-24, More reliable from 2026-10-31, Implantation from 2026-10-16, Implantation up to 2026-10-22.Source: hand calculation in content.mdx: expected period = ovulation + 14 days (ACOG); Wilcox 1999 and 2001
  3. What do you know? Day of sex, Day you had sex 2026-09-20 gives Test on or after 2026-10-11.Source: NHS, Doing a pregnancy test: at least 21 days after unprotected sex; September 20 + 21 days
  4. What do you know? Last period, First day of your last period 2026-01-01, Cycle length (days) 35 gives Test on or after 2026-02-05, Ovulation 2026-01-22.Source: hand calculation in content.mdx: a 35-day cycle, so ovulation on day 21 and the period on day 35

How the test date is worked out

All dates are calendar days.

From your last period (first day d, cycle length c days):

  • expected period = d + c days;
  • ovulation = expected period − 14 days, the average in ACOG's guidance.

From your ovulation day (o):

  • expected period = o + 14 days.

Then, in both cases:

  • test on or after the expected period, the first day of the missed period (NHS);
  • more reliable from 7 days after that: by then, at most 3% of pregnancies are too early to detect, against about 10% on the first day (Wilcox and others, 2001);
  • implantation window = ovulation + 6 days to ovulation + 12 days (Wilcox and others, 1999). A test cannot turn positive before implantation.

From the day you had sex (s), when you do not know your period date: test on or after s + 21 days (NHS).

Assumptions

  • Ovulation is 14 days before the expected period. Real cycles vary, so the missed period can come later than predicted.
  • The detection figures come from a very sensitive laboratory test. Home tests are less sensitive, so they can miss more pregnancies on the first day.

This page is for information only. It is not medical advice. See a health care professional for a blood test or if you are unsure about a result.

Worked examples by hand

Last period September 1, 2026, 28-day cycle. Expected period: September 1 + 28 days = September 29, 2026, so test on or after September 29. More reliable from September 29 + 7 = October 6. Ovulation: September 29 − 14 = September 15. Implantation window: September 15 + 6 = September 21 to September 15 + 12 = September 27.

Ovulation on October 10, 2026. Expected period: October 10 + 14 = October 24: test from then. More reliable from October 31. Implantation: October 16 to October 22.

Sex on September 20, 2026, period date unknown. September 20 + 21 days = October 11, 2026.

Last period January 1, 2026, 35-day cycle. Expected period: January 1 + 35 days = February 5, 2026. Ovulation: February 5 − 14 = January 22.

Other questions people ask

How soon can I take a pregnancy test?

The NHS says most tests can be used from the first day of a missed period. If you do not know when your period is due, test at least 21 days after you last had unprotected sex. A test cannot turn positive before the embryo implants, which is usually 6 to 12 days after ovulation.

Why can a test be negative on the day of my missed period?

Because implantation does not always happen before then. Wilcox and others (2001) found that about 10% of pregnancies had not implanted by the first day of the missed period, so even a perfect test could miss them. One week later, at most 3% were still undetectable.

What is implantation and when does it happen?

Implantation is when the embryo attaches to the lining of the uterus and starts making hCG, the hormone pregnancy tests detect. In a study of pregnancies that lasted at least 6 weeks, it happened 6 to 12 days after ovulation, and in 84% of them on day 8, 9, or 10 (Wilcox and others, 1999).

I got a negative result but my period has not come. What now?

Test again in a few days to a week, when more pregnancies can be detected. Irregular cycles, a late ovulation, or testing too early can all give a negative result. If your period still does not come, talk with a health care professional.

Is a blood test more accurate than a home test?

A blood test at a clinic measures hCG directly, but it still cannot detect a pregnancy before implantation. Ask a health care professional if you need an early or exact answer.

Does the time of day matter?

Follow the instructions that come with your test, including any advice on the time of day to test.