Home tests detect hCG, a hormone made after implantation. Levels double every 2–3 days in early pregnancy, so testing too early can give a false negative. Testing with first-morning urine on the day of your missed period is most reliable.
How to use the Pregnancy Test Calculator
- I know my…
- First day of your last period
- Average cycle length
- Date of unprotected sex
Results update as you type, and every field accepts the units shown in its menu.
How it works
Choose what you know and enter the date. If a test is negative but your period still does not come, test again in 2–3 days.
Inputs explained
| Field | What to enter |
|---|---|
| I know my… | Choose one: Last period and cycle length, Date of unprotected sex, Ovulation date |
| First day of your last period | A date |
| Average cycle length | In days |
| Date of unprotected sex | A date |
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
Ovulation ≈ LMP + cycle − 14 (or the date you entered)
Earliest sensitive test ≈ ovulation + 10 days
Reliable test = first day of missed period (≈ ovulation + 14 days)
Worked example
Inputs — I know my…: Last period and cycle length; First day of your last period: 2026-10-07; Average cycle length: 28 days.
Results — Ovulation (estimate) = Wed, October 21, 2026; Earliest test (sensitive early test) = Sat, October 31, 2026; Reliable test date = Wed, November 4, 2026; Blood test could detect pregnancy from = Thu, October 29, 2026.
Key terms
- hCG
- Human chorionic gonadotropin, the pregnancy hormone.
Frequently asked questions
How soon can I take a pregnancy test?
Some sensitive tests detect hCG 10 days after ovulation, but the most reliable day is the day of your missed period.
Can a test be falsely negative?
Yes – testing too early or with diluted urine. Retest after 2–3 days.
Can it be falsely positive?
Rarely – after a recent pregnancy loss, with fertility drugs containing hCG or with some rare conditions.