Build vs. Buy
Slide the inputs. Watch the two curves. The year they cross is the year building pays off.
Verdict
Break-even: Year 3
Total Buy
$0
Total Build
$0
Delta
-
What this models, and what it does not
What it models. Buy is a flat annual cost: seats x monthly price x 12, plus any annual enterprise license. Build is a front-loaded cost: Year 1 is the full engineering team working on the product; Year 2 and onward are the team's time at a reduced maintenance factor (default 30%, meaning the team spends about a third of their ongoing time keeping the product alive).
What it does not model. Benefits and overhead on top of salary. Hiring ramp time. Opportunity cost of what the engineers could have built instead. Vendor price increases. Churn. Integration headaches. The one-time cost of switching providers when you outgrow the SaaS. This is a conversation-starter, not a procurement decision.
Why break-even matters. If the curves never cross inside your horizon, buying is cheaper for the period you are planning. If they cross fast, building pays off, assuming you can actually build and maintain it. The maintenance slider is the honest lever here: drop it to 15% if your team barely touches it after Year 1, push it to 80% if the thing constantly breaks.