Internal developer platform ROI should be framed as a three-year total cost of ownership problem, not a morale memo. If you build, you fund a platform team to create and then operate the IDP as an internal product for years. If you buy, you pay a vendor license plus integration work and move that headcount to product. Either way, the platform has to save more engineering time than it costs.
Direct answer: Build only when the measured time saved is worth more than the extra cost of building over buying. In the worked example below (100 engineers, an assumed $91/hour loaded cost), building costs about $1.8M more than buying over three years, so it needs to save roughly $600k a year, about 1.3 hours per engineer per week, just to break even. If you cannot show that saving in a pilot, buy, and spend the engineering time on your product.
A baseline to start from: the median US wage for software developers was $135,980 in May 2025 (BLS). This model assumes a loaded cost (salary plus benefits and overhead) of $190k a year, about $91 an hour over 2,080 hours; replace it with your own payroll figure. On that assumption a 6-engineer platform team costs $1.14M a year and an 8-engineer team $1.52M, and those costs recur for as long as the platform needs maintaining.
On the buy side, commercial IDP vendors usually price per developer or by tier, so get quotes for your own headcount rather than relying on a published range. Backstage, the open-source developer portal created at Spotify and now a CNCF project (backstage.io), removes license fees but still needs engineers to integrate, host and maintain it. Add the CI minutes, artifact storage and telemetry the platform will consume to both columns.
Internal developer platform ROI
Start with the rule: an IDP is justified when the extra developer productivity it creates is worth more than the extra cost of delivering and operating it. For a 100-engineer org, 1 hour a week saved equals 5,200 hours a year. At the assumed $91 an hour that is about $473k a year in productivity value, and two hours a week is about $946k. Those dollars only count if the saving actually shows up in delivery metrics.
Compare three-year scenarios (illustrative assumptions, not quotes). Example A (build): 8 engineers for 9 months = 8 × $190k × 0.75 = $1.14M of year-one labor, plus an assumed $200k of infrastructure and $300k of integration and tooling, about $1.64M in year one; then 4 engineers to operate it at $760k a year. Three-year TCO is about $3.16M. Example B (buy): an assumed $400k a year license, $100k onboarding and $50k infrastructure, $550k in year one and $400k a year after, about $1.35M over three years. Building has to deliver more than $3.16M − $1.35M = $1.81M of value over three years, roughly $600k a year in productivity gains.
Hidden costs matter: retraining teams on new CI/CD flows, migrating integrations (secrets management, SSO, artifact repositories), and handling platform incidents all take platform-team time that early plans tend to leave out. A vendor absorbs some of that work and operational risk. CI minutes and egress also grow with the number of builds, so track them per month from the start of the pilot.
Don't build an IDP because it's 'strategic'; build it when the math shows a sustained, measurable productivity delta equivalent to at least one full engineer per 20 product engineers.
