Home COVID tests work by swabbing your nose, mixing the sample with a liquid reagent, and placing drops on a test strip that shows results in about 15 minutes. The process is straightforward, but small details in timing, technique, and interpretation make a real difference in whether your result is accurate.
What You Need Before You Start
Each test kit comes with nasal swabs, a small tube of liquid reagent, and a test cassette with a results window. Before opening anything, check the expiration date on the box. Many home tests have had their shelf lives extended by the FDA, so even if the printed date has passed, your kit may still be valid. You can look up your specific test on the FDA’s “At-Home OTC COVID-19 Diagnostic Tests” page, which lists extended expiration dates by manufacturer and test name.
Temperature matters more than most people realize. Tests are designed to work between roughly 59°F and 86°F. If your kit was delivered in freezing or very hot weather, bring it inside and leave it unopened at room temperature for at least two hours before using it. A test that sat outside in extreme heat for several days may no longer be reliable, and you’re better off using a different one.
Step-by-Step Testing Process
Blow your nose gently before you begin, then open the swab package without touching the soft tip. Insert the swab about half an inch to three-quarters of an inch into one nostril (your kit’s instructions will specify the exact depth) and rotate it against the inside wall for about 15 seconds. Repeat in the other nostril with the same swab.
Drop the swab into the tube of reagent liquid and swirl or rotate it as directed, usually for 30 seconds or so. The reagent breaks open any virus particles and exposes the proteins inside. Squeeze the tube gently against the swab as you pull it out to extract as much liquid as possible, then apply the specified number of drops to the sample well on the test cassette. Set a timer for the time listed in your instructions, typically 15 minutes. Reading the result too early or too late can give you a wrong answer.
Adding a Throat Swab
Some people swab their throat in addition to their nose, and research supports this approach. A study conducted during Omicron predominance found that combining nose and throat swabs increased sensitivity by about 15 to 21 percentage points compared with a nasal swab alone. Throat swabs on their own actually outperformed nasal swabs when collected by healthcare workers, though for self-collected samples in symptomatic people, nasal swabs were more sensitive (about 72% versus 58%). If you decide to try both, swab your throat first, then use the same swab in your nostrils, so you don’t introduce nasal material into your throat. Note that most test kit instructions only authorize nasal swabbing, so this is an off-label technique.
When to Test for the Most Accurate Result
Timing is one of the biggest factors in whether a home test catches an infection. If you have symptoms, test as soon as they appear. The sensitivity of rapid antigen tests jumps significantly when symptoms are present: about 85% accurate at detecting a contagious infection in symptomatic people, compared with just 45% in people without symptoms.
If you were exposed to someone with COVID but feel fine, wait five days before testing. Testing too early after exposure often produces a false negative because the virus hasn’t replicated enough to be detectable yet. COVID’s incubation period, the time between exposure and the start of symptoms, can vary, but five days gives the virus enough time to reach levels a rapid test can pick up.
Reading Your Results
The results window will show lines similar to a pregnancy test. A control line (usually labeled “C”) should always appear. This confirms the test ran correctly. A second line near the “T” marker means the test detected COVID proteins in your sample.
A faint test line is still a positive result. The darkness of the line reflects the amount of virus in your sample, so a faint line could mean you’re in the early or late stages of infection, but it still means viral particles are present. As Johns Hopkins infectious disease specialist Amesh Adalja has explained, a lighter line reflects less viral material, which could indicate either rising or diminishing contagiousness, but you should treat it the same as a bold line.
If no control line appears, or if lines show up in the wrong locations, the test is invalid. Don’t try to interpret it. Discard the cassette and run a new test with a fresh kit.
What to Do After a Negative Result
A single negative result doesn’t rule out COVID, especially if you tested without symptoms. Based on findings from a National Institutes of Health study, the FDA recommends repeat testing every other day when the first result is negative. The specific guidance: test at least twice if you have symptoms, and at least three times if you don’t. So a person with a cough who tests negative on Monday should test again on Wednesday. Someone without symptoms who was exposed should test on three separate days spaced 48 hours apart.
This repeat-testing protocol exists because rapid antigen tests have limited sensitivity early in infection. Overall sensitivity against a PCR reference is about 47%, which sounds low, but that number includes people tested very early or late in their illness. Against viral culture (which measures whether someone is actually contagious), sensitivity is around 80%. In practical terms, rapid tests are better at telling you whether you’re contagious right now than whether you’ve been infected at all.
How the Test Actually Works
The test strip is coated with antibodies designed to grab onto a specific protein found inside the SARS-CoV-2 virus, called the nucleocapsid protein. When you mix your swab with the reagent, the liquid breaks the virus apart and exposes this protein. As the liquid moves along the strip, any viral protein gets caught at a specific spot and triggers a visible color change, producing that second line. The whole process is called a lateral flow assay, and it’s the same basic technology used in home pregnancy tests and rapid strep tests.
Where to Get Tests
Home COVID test kits are sold at most pharmacies without a prescription. Your health insurance may cover the cost of both at-home kits and in-person testing. Some state health departments still offer free testing programs, which you can find through your state’s public health website. Prices for over-the-counter kits typically range from about $10 to $25 for a two-pack, with molecular home tests (which use a different, more sensitive technology) costing more.
Common Mistakes That Affect Accuracy
The most frequent errors are simple ones: not swabbing long enough, not rotating the swab firmly against the nasal wall, or using too few or too many drops of the sample liquid. Each brand has slightly different instructions for drop count and timing, so read yours even if you’ve used a different brand before.
Other pitfalls include testing immediately after eating, drinking, or using nasal spray, which can dilute or contaminate the sample. Storing tests in a car glove compartment during summer or winter exposes them to temperatures well outside their working range. And reading results after the maximum time window (often 30 minutes) can produce faint “evaporation lines” that look like a weak positive but aren’t meaningful.
If you get a negative result but still feel sick, the most useful next step is to repeat the test in 48 hours. If you need a definitive answer sooner, PCR tests at clinics and pharmacies remain more sensitive than rapid antigen tests, particularly in the first day or two of symptoms.