I think 12% is the positive rate among patients without symptoms at the time of the test, so if you want to extrapolate from there to an estimate of your chance of experiencing no symptoms, you’ll first need to estimate how many of those people were in fact presymptomatic.
edit: also, if I’m reading your comment right, I think you’re interpreting 12% as the proportion of positive cases that had no symptoms, whereas it’s actually the proportion of people without symptoms who tested positive:
~1-in-8 UCSF patients w/ NO Covid symptoms are testing +
I think 12% is the positive rate among patients without symptoms at the time of the test, so if you want to extrapolate from there to an estimate of your chance of experiencing no symptoms, you’ll first need to estimate how many of those people were in fact presymptomatic.
edit: also, if I’m reading your comment right, I think you’re interpreting 12% as the proportion of positive cases that had no symptoms, whereas it’s actually the proportion of people without symptoms who tested positive: