Build vs. Buy ROI Calculator — Free Tool

What are you deciding on?e.g. "CRM platform", "lead-routing engine"

Horizon

Build it

In-house. Your team owns the code, the bugs, the roadmap, and the maintenance burden.

Initial development cost salary × months × people, all-in

Months to deliver until in production for users

months

Annual maintenance bugs, deps, infra, ongoing changes

$/yr

Opportunity cost engineering time not spent on core product

$/yr

Risk overrun % chance the build runs 1.5x cost

A vendor's product. Faster to value, no maintenance, but you rent the capability and they raise prices.

Annual subscription at today's price

$/yr

Setup & integration one-time, including internal time

Months to deliver implementation to production

months

Annual price increase 8–12% is typical for SaaS

%/yr

Switching cost if you'd ever need to leave

Don't underestimate the build. Most internal estimates miss the long tail — onboarding, docs, on-call, compliance, the second person who has to learn it. Pad your numbers, not theirs.
The vendor's price will rise. 8% compounded over 5 years is +47%. The headline price is not the price you'll pay in year three, four, or five.
Time-to-value is a real cost. If Build delivers in month 9 and Buy delivers in month 2, that's seven months of foregone benefit. The line chart shows you what that looks like.
Look at the crossover, not the total. If Build "wins" by year five but you're not sure you'll be on this stack in year five, the total is misleading. Who wins by year two matters more.
Read the sensitivity panel. If the answer flips when your build runs 1.2x over (which it will), the verdict isn't really build — it's "build, conditional on flawless execution."