On average, the figure is about €2500 (about $3900).
That's per day. Toss in a coin, so the story goes, and you'll return to bella Roma.
Who could resist a line like that?
The tradition of tossing a coin into the fountain goes back to time immemorial, later embedded in the 1950s film Three Coins in the Fountain.
The cash is raked up by city workers and delivered to Caritas, a Catholic non-profit charity.
Except that which went into the pocket of Roberto Cercelletta, a mentally unstable and unemployed local who would visit the fountain by night and do a little fishing with a magnet – and pocket anything up to $1000 per night.
The advent of non-magnetic euro coinage made the job more difficult and Cercelletta was forced to wade into the fountain, but it was larceny on a grand sale.
Cercelletta's coin collecting went on for 34 years while police and city authorities turned a blind eye until he was arrested in 2002.
Neither history nor superstition should dim the spectacle of one of the most beautiful baroque fountains you'll ever see.