In almost two decades of PHP programming, I can remember that I was 'forced' by a webhost to update my code only once. They went from PHP5 to PHP7 - if I recall

In almost two decades of PHP programming, I can remember that I was 'forced' by a webhost to update my code only once. They went from PHP5 to PHP7 - if I recall correctly - and I had to change some MySQL function calls to MySQL PDO. It was slightly more work than changing function calls, but if my code had been object oriented at that time, it would have cost me one hour max. Your mileage may vary for bigger code bases. Edit: okay, make that two hours.