Build vs Buy Calculator
Total cost of ownership for software decisions, over your horizon.
Cheaper option over your horizon
Estimates for planning only, not financial advice.
Build vs buy analysis answers one question: over the years you will actually use the software, does developing it in-house or purchasing a vendor product cost less in total? The honest math is total cost of ownership, not the first invoice. A $120,000 build with $24,000 a year in maintenance costs $240,000 over 5 years, while a $25,000-a-year license with a $40,000 implementation costs $165,000 over the same period. Same problem, $75,000 apart before you count the intangibles.
How to Use This Calculator
Enter your comparison horizon first, usually 3 to 5 years. On the build side, put the full upfront development cost (loaded team cost, not just salaries) and the annual maintenance budget. On the buy side, enter the total annual license for all seats or usage, the one-time implementation and migration cost, and the vendor\'s annual price growth, because renewals rarely stay flat. The calculator compounds the license growth year by year and declares the cheaper option with the dollar gap.
Set the horizon to how long you realistically expect to use the software, 3 to 5 years for most tools.
Fill the build side with loaded costs: salaries plus benefits, recruiting, infrastructure, QA, and yearly maintenance at 15 to 25 percent of the build cost.
Fill the buy side with the full license cost for all users, implementation, migration, training, and an annual uplift of 3 to 7 percent. Read the winner, the gap, and the year-by-year breakdown. If the gap is under 15 percent, treat the decision as strategic rather than financial.
The Total Cost of Ownership Formula
Both sides get every cost line they usually hide. Building hides maintenance, security patching, and the opportunity cost of engineers not working on your product. Buying hides implementation, integration, training, and renewal uplifts. The growth term matters more than people expect: a $25,000 license growing 5 percent a year costs $138,140 over 5 years, not $125,000. At a 10 percent uplift it is $152,577. Always model the renewal curve, because vendors model it too.
Worked Example
A 40-person company needs a custom reporting portal. Build quote: $120,000 upfront with $24,000 a year in maintenance (20 percent, the middle of the standard range). Buy option: $25,000 a year in licenses with a $40,000 implementation and 5 percent annual uplift. Over 5 years, building costs $120,000 + $120,000 = $240,000. Buying costs $40,000 + $25,000 + $26,250 + $27,563 + $28,941 + $30,388 = $178,141. Buying wins by about $61,859, and it ships in weeks instead of quarters. Flip the horizon to 10 years and building pulls ahead, which is exactly why the horizon choice drives the answer.
When the Math Says Buy but You Should Build
Three situations override a buy verdict. First, the software is your competitive edge: if the tool is what customers pay you for, owning it is strategy, not cost. Second, no vendor fits without contorting your workflow, and the customization fees erase the savings. Third, per-seat pricing punishes your growth model: a $50-a-seat tool is cheap at 20 seats and brutal at 2,000. In those cases, run the calculator again with your projected year-5 headcount in the license field and watch the verdict change.
| Signal | Usually means |
|---|---|
| Tool is back-office plumbing (payroll, ticketing, email) | Buy, almost always |
| Tool is customer-facing and differentiating | Build, or buy core plus custom layer |
| Requirements are standard and stable | Buy |
| Requirements are unusual or change fast | Build |
| Per-seat cost explodes with headcount | Build or negotiate flat pricing |
Common Mistakes in Build vs Buy
The classic error is comparing the build quote against year-one license cost and calling it done. The second is forgetting maintenance on the build side: unmaintained internal tools rot within two years as dependencies age and browsers change. The third is ignoring time to value. A vendor tool live in month two starts paying back 10 months before a build that ships in month twelve. If the problem costs you $5,000 a month, that delay is a $50,000 hidden line in the build column. For the payback math on either option, our payback period calculator and ROI calculator turn the totals into investment language your CFO already speaks, and our present value calculator discounts multi-year costs properly.
Estimates for planning only, not financial advice.
Frequently Asked Questions
What is build vs buy analysis?
Build vs buy analysis compares the total cost of developing software in-house against purchasing a ready-made product over the same time horizon. Building means paying developers, designers, and ongoing maintenance yourself. Buying means paying license or subscription fees plus implementation, training, and integration. The honest comparison is total cost of ownership over 3 to 5 years, not the first-year price tag.
What costs should I include on the build side?
Include the full loaded cost of the team (salaries, benefits, recruiting), design and product management time, infrastructure and hosting, QA and security reviews, and ongoing maintenance, which typically runs 15 to 25 percent of the initial build cost per year. Most teams underestimate maintenance. A $120,000 build usually needs $18,000 to $30,000 a year just to stay current, patched, and supported.
What hidden costs hide on the buy side?
Implementation and data migration fees, integration work with your existing stack, per-seat or usage-based price increases as you grow, training time for your team, and the cost of working around features the vendor does not offer. Ask vendors for a 3-year price lock in writing, because list prices at renewal time are where buy-side budgets usually break.
When does building usually win?
Building wins when the software is core to your competitive advantage, when no vendor product fits your workflow without heavy customization, or when per-seat licensing would explode with your headcount. If the tool is your product differentiator, owning the code is worth the premium. If it is back-office plumbing like payroll or ticketing, it almost never is.
How do I account for time to value?
Add it as a cost line both sides can feel. A vendor tool can be live in weeks; an in-house build takes months, during which the problem it solves keeps costing you money. If slow invoicing costs you $5,000 a month in late payments and the build takes 6 months while the vendor deploys in 6 weeks, that gap is a real $20,000-plus difference in the buy column.
Should I include the opportunity cost of my developers?
Yes, and this is the line most build estimates skip. Every engineer-month spent rebuilding a commodity tool is a month not spent on your product. Value it at the revenue or cost savings your product roadmap would have delivered, or at minimum at the loaded cost of the team. When leadership sees what the build displaces, the decision often makes itself.
What time horizon should I compare over?
Three to five years is the standard. One year flatters buying (low upfront) and punishes building (all cost, no amortization yet). Beyond five years, technology assumptions get shaky: vendors get acquired, pricing models change, and your requirements drift. Run the math at both 3 and 5 years. If the winner flips between them, the decision is genuinely close and the tiebreakers are strategic, not financial.
How do switching costs factor in?
Add an exit cost to the buy side: data extraction, retraining, and the operational risk of migrating off a vendor later. Vendor lock-in is a real liability, strongest with proprietary data formats and deep workflow integration. Mitigate it up front by confirming data export formats and API access before you sign, and price a hypothetical year-4 migration at 30 to 50 percent of the original implementation cost.
Can a hybrid approach work?
Often it is the best answer. Buy the commodity core and build only the differentiating layer on top through the vendor API. You get the vendor's maintenance and security updates for 90 percent of the system while owning the 10 percent that makes you different. Price the hybrid as its own option in the calculator: vendor license plus a smaller build budget for the custom layer.
What is the 15 to 25 percent maintenance rule?
Industry experience says maintaining custom software costs roughly 15 to 25 percent of its initial development cost every year: bug fixes, security patches, dependency upgrades, OS and browser changes, and small feature requests that never stop. A $120,000 build at 20 percent needs $24,000 a year. Over 5 years that is $120,000 in maintenance alone, matching the original build cost.