Build vs Buy Software Calculator
Compare the cost and long-term impact of building custom software versus buying an existing solution.
Build vs buy details
This calculator auto-updates when values change.
Compare custom build cost with subscription cost over a chosen period.
Buy is cheaper
£12,800
Build total is about £164,000 versus buy total of £151,200 over 3 years.
Build total
£164,000
Buy total
£151,200
Maintenance included
£54,000
Cost difference
£12,800
About This Build vs Buy Software Calculator
Build vs Buy Software Calculator is designed for practical business planning, not abstract spreadsheet modelling. It turns a common commercial decision into a clearer number so you can compare options before committing time, money, or client expectations.
Building software can create control and differentiation, but buying can reduce risk, speed up launch, and avoid hidden maintenance costs.
The result is an estimate based on the inputs you provide. Real outcomes depend on taxes, contracts, payment timing, market demand, client behaviour, and operating costs.
Practical Example
A custom build may cost GBP 85,000 upfront plus maintenance, while a subscription may look expensive monthly but remain cheaper over three years.
The useful part is not only the headline result. The supporting breakdown shows which assumption drives the outcome and where a small change would make the biggest difference.
How to Use This Strategically
Use the result to structure the decision. If building is more expensive, it may still be right when the software is core to the business; if not, buying often preserves focus.
Run a conservative scenario and an optimistic scenario. If the decision only works under perfect assumptions, it probably needs a stronger margin of safety.
Common Mistakes to Avoid
Avoid using best-case inputs for billable time, conversion, churn, client stability, or costs. Business calculators are most useful when they reveal risk early rather than confirming a plan you already wanted to believe.
If the result affects pricing, hiring, contracts, product direction, or cash reserves, compare it with real accounting data and professional advice before making a major decision.
How to Use This Calculator
- 1
Enter realistic inputs
Use current numbers where possible, and avoid best-case assumptions unless you are deliberately testing upside.
- 2
Review the headline result
Start with the main result, then compare the supporting metrics underneath it.
- 3
Test a second scenario
Change the weakest assumption to see whether the decision still works.
- 4
Use the output for planning
Treat the result as a planning signal, not as a guaranteed business outcome.
Frequently Asked Questions
What does the Build vs Buy Software Calculator do?v
Compare the cost and long-term impact of building custom software versus buying an existing solution.
Are the results exact?v
No. They are estimates based on the numbers you enter and should be checked against real business records.
Can I use this for client or investor decisions?v
Yes as a planning aid, but important decisions should be supported by accounting, legal, tax, or commercial advice where relevant.
Why should I test multiple scenarios?v
Business plans are sensitive to assumptions. A low, expected, and high scenario gives a more useful range than one perfect-looking result.