Build vs buy, over three years
Is it cheaper to keep paying per seat or to have something built?
Subscriptions charge you more as you grow. Custom software costs more at the start and then stops scaling with headcount. Somewhere between those two shapes there is a crossing point, and it is usually the whole decision.
This finds that crossing point for your numbers over thirty-six months.
How this is calculated:
The buy path grows seats in a straight line from today's count to your three-year count, and charges your per-seat price every month along the way.
The build path charges the one-time build cost in month zero, then the monthly running cost you enter for hosting, maintenance and changes.
Break-even is the first month where the running total of building is lower than the running total of buying. If that never happens inside thirty-six months, it says so rather than extrapolating further.
Questions people ask about this tool:
What should I put for the build cost?
A real quote if you have one. If you do not, this tool is better used backwards: enter the build cost that would break even at a month you would accept, and you have the number a proposal has to beat.
What goes in the monthly running cost?
Hosting, third-party services the system depends on, and the ongoing time to change it. Software that nobody maintains stops being used, so a running cost of zero is not a real answer.
Cost is not the only factor, is it?
No. Fit, speed and who owns the result usually matter more. This answers only the money question, which is the one that is actually calculable.