I'm looking to move from a 10 year one-time license + yearly maintenance pricing model to a monthly subscription fee model (3 or 5 years minimum contract duration). Ideally I'm looking for a simple formula that would convert from one model to another.
Perhaps I am not understanding your phrase or what you're looking for. A simple formula would be 10 years divided by 120 (to get the fee per month). To keep all things equal, this number is now your monthly subscription fee.
Feel free to drop me a note if there is something we can clarify.
All the best,