Let me say the unpopular thing first, since I'm the person who builds custom software for a living: most of the time, you should buy. If a category is well served and the problem isn't what makes you different, license the tool and get on with your life. Building something you could have bought is a great way to spend six months reinventing a wheel that already rolls fine.
But sometimes buying is the expensive decision wearing the safe decision's clothes. The trick is knowing which situation you're in before you sign a three-year contract or greenlight a build.
Buy when the problem is a commodity
Buy when what you need is broadly the same as what every other company needs. Email, payroll, video calls, most of accounting - solved. You are not going to out-engineer a company whose entire existence is that one product, and you shouldn't try. Rent it, integrate it, move on.
Build when the process is the business
Build when the workflow is the thing you actually do - close enough to your core that owning it is a real advantage. A few signals you're in build territory:
- The tool solves maybe 40% of the job and your team handles the other 60% in spreadsheets and side channels.
- Per-seat pricing means every new hire grows your software bill - you're being taxed for succeeding.
- Your data is trapped inside a vendor's boundary and you can't get it where it needs to go.
- You're bending your process to fit the software instead of the other way around.
When several of those are true, buying isn't cheaper. It just moves the cost somewhere you're not looking.
The costs nobody puts in the spreadsheet
Both sides have hidden costs, and the honest comparison includes them. Buying hides the integration tax, the per-seat compounding, and the quiet loss of control - you inherit a roadmap set by someone optimizing for their average customer, not for you. Building hides maintenance: the day you ship is the day you own every bug and every change, forever. Anyone who tells you a custom build is 'done' at launch is selling you the fun part and skipping the rest.
Own the things that are you. Rent the rest. Most of the regret I see comes from getting that one line backwards.
A test that takes thirty seconds
Ask yourself: if this system vanished tomorrow, would we lose something that makes us us? If yes, lean toward owning it. If it's just plumbing every company has, rent it. And whoever you ask for advice - a firm like mine included - push them to make the honest call, not the one that bills the most. If they can't say 'buy this, don't hire us for it,' find someone who can.