Compare true operating cost.
Subscription growth, implementation, migration, workaround labour and admin sit on the buy side. Build cost, hosting, support, rollout and ongoing ownership sit on the build side.
Free tool · Build vs Buy Calculator
Should you buy it, build it, or split the difference?
Compare SaaS, custom software and a hybrid route using your own costs, workarounds, growth and operating constraints. See total cost, workflow fit and the exact assumptions that would flip the decision.
Total cost1-5 year entered TCO
More than two routesBuy · Build · Hybrid · Discovery First
Flip pointsSee which assumption changes the answer
Your decision
Put both options on the same page.
The calculator uses only the figures and constraints you enter. Blank means unknown; enter 0 only when a cost or workload genuinely does not apply. The cost model is calculated in your browser; the optional decision summary receives only the resulting figures and constraints.
01 · Context
What are you trying to solve?
Required only when buy-side workaround or admin time is above 0.
Optional. Used to show time-to-value exposure, not hidden inside TCO.
02 · Buy
Your figuresOff-the-shelf / SaaS
03 · Build
Your figuresCustom software
04 · Strategic fit
Your assumptionsWhere the numbers do not tell the whole story
How standard is this workflow?
How well does the buy option fit?
How important is data / permission control?
How integration-heavy is the workflow?
How urgent is time-to-value?
How often does the workflow change?
How painful would vendor lock-in be?
Can you own a custom system after launch?
Build vs buy decision
Your route, with the assumptions exposed.
How it decides
The cheapest number is not automatically the right answer.
Separate commodity from advantage.
A standard workflow with a good SaaS fit should usually lean toward buying. A highly specific or differentiating workflow can justify ownership even when the first-year build cost is higher.
See what changes the answer.
The scenario lab exposes thresholds such as the SaaS monthly cost, workaround time or build budget at which the economics switch sides. That makes the assumptions discussable instead of hiding them inside a score.
Already know the direction?
Turn the decision into something buildable.
If the right answer is custom or hybrid, the next useful step is to define the workflow, first release, integrations, acceptance checks and unknowns before anyone starts coding.
Free next stepUse the Custom Software Brief Builder.
Build the brief →Convert the business problem into a provider-neutral brief you can take to any developer or agency.
FAQ
A few important boundaries.
Does lower TCO automatically win?
No. Economics are one part of the decision. Workflow fit, control, time-to-value, integrations and ownership can make the cheaper route the wrong operational choice.
Does ZappFlow estimate SaaS or development prices?
No. The calculator uses the figures you enter. Blank means unknown and is never silently treated as £0. Enter 0 only when a cost genuinely does not apply.
Why can the answer be Hybrid or Discovery First?
Because build versus buy is often not binary. Commodity capabilities can be bought while a differentiated workflow is built around them. If the evidence is incomplete or contradictory, more discovery is safer than a forced recommendation.