The RIVM, the Dutch public health agency, referred me to this paper after I asked about combinations of symptoms (their website[1] only lists individual symptom occurrence percentages for seropositive and seronegative cases). Given that most people will not read a scientific paper and calculate that formula, I thought this might be helpful to others.
Disclaimer, as is also written on the site in bold and red: this is NOT validated or endorsed by the authors of that paper and this is NOT a replacement for a real COVID-19 test! The point is to give a rough indication using the same phrasing and exact model from the paper.
[1] https://www.rivm.nl/pienter-corona-studie/resultaten (Dutch, see "Tabel 1")