# Pregnancy Test Calculator (When to Test)

URL: https://speedycalculator.com/calculators/health/pregnancy-test/
Last updated: 2026-10-30

> The pregnancy test calculator tells you the earliest day a home pregnancy test might be positive and the day it becomes reliable, from your last period and cycle length, the date you had sex or your ovulation date.

## Inputs

- I know my…
- First day of your last period
- Average cycle length (days)
- Date of unprotected sex

## Results

- Ovulation (estimate)
- Earliest test (sensitive early test)
- Reliable test date
- Blood test could detect pregnancy from

## 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)
```

## Explanation

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

FieldWhat to enterI know my…Choose one: Last period and cycle length, Date of unprotected sex, Ovulation dateFirst day of your last periodA dateAverage cycle lengthIn daysDate of unprotected sexA 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.*

## 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.

## FAQ

**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.


## Sources

- [U.S. FDA – Pregnancy tests](https://www.fda.gov/medical-devices/home-use-tests/pregnancy)
- [Cole LA. The utility of six over-the-counter home pregnancy tests. Clin Chem Lab Med, 2011](https://pubmed.ncbi.nlm.nih.gov/21561363/)