AI Build vs Buy Calculator (3-year TCO: subscription vs self-built tool)

How it works

Total cost of ownership (TCO) over the years compared. Subscription = users × price × 12 for each year, with the price rising by the yearly percentage (year 1 at today’s price). Self-build = development cost + monthly hosting/API × 12 × years + yearly maintenance (a percentage of the development cost) × years. The break-even user count is the number of users at which the subscription total equals the self-build total. Staff time to run either option, and money’s time value, are not included.

⚠ Estimates for information only — not financial advice.

FAQ

What maintenance percentage should I use?

Software needs fixes, security updates, model and API changes. Ask your developers; many teams plan 15–25% of the build cost a year, but your figure may differ.

What does the comparison leave out?

Time to build (you pay for a subscription from day one but a self-built tool takes months), the risk of the project slipping, data-security requirements and the value of features only one option has.

Checked 10 Nov 2026. Total cost of ownership: sum of acquisition and operating costs over the period (Gartner’s TCO concept); yearly maintenance as a share of build cost is your own estimate.