A family member didn't test positive until the 5th day after symptoms started. He took a Covid test every day for 4 days and all were negative. On the 5th day, it was positive.
Just in the last few days, I told several friends about this and they both thought they had colds and both turned out to have Covid. One had just tested once, but tested again on my recommendation because she lives with her elderly mother. It was Covid.
The other had already tested 3x, but sent me a sad message that the 4th test was "the charm." 
Not trying to be a downer, but it is critically important to take multiple tests for at least 5 days after symptoms start so early interventions, such as Paxlovid or monoclonal antibodies, can be given in time to prevent more serious illness.
Also, multiple tests are needed anyway because rapid tests have a lot of false negatives.
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