Signal is a communication application. It comprises of client programs, server code and the infrastructure that runs the server code.

There is Signal Foundation behind this that takes care of the development, maintenance and operating this setup. Originally, it got some startup money and currently it receives some money as donations from the users.

As per the 990 form report from 2019, the foundation had:

  • income from contributions: $17.5e6
  • total expenses: $13.5e6
    • personal: $5.8e6
    • infrastructure: $3.8e6
  • 5e5 annual users (source)
    • 10e6 downloads
    • 15e6 active users per Wikipedia interpolation
      • more likey just 10e6 given geometric growth
    • the reported number in 2022 is 40e6 users

So the 2019 data gives us the expense is between $0.38 /user/year and $27 /user/year. The former is the worst case estimate when development/maintenance froze and just the infrastructure necessary for the communication was kept up. The latter are total expenses spread over the minimal estimate of active users.

This is not very economic estimate, it spans roughly two decimal orders of magnitude, despite that say that some $3 /user/year donations are necessary to make Signal sustainable in the current form.

Update 2023-10-19

Signal blogs about $14e6 / year on infrastructure costs and $19e6 / year on personal costs (~50 FTEs), the article writes about 100kHz requests.

Assuming, 30 transactions/user/day and 2 requests/transaction, it estimates some 144e6 active users. Or $0.2 / user / year.