How long does it take to build custom software?

For a first release of a real product with a backend, accounts and an admin: three to five months. A focused internal tool can be six weeks. A regulated financial product is a year. Anyone giving you a precise number before understanding your data model is guessing.

Where the time actually goes

Building the screens is rarely the long part. The long parts are:

Deciding what it is. The clearer the specification, the shorter the build — and most projects start far less clear than they believe. A week spent on scope saves a month of rework.

The data model. Get this wrong and every later feature fights it. This is the single most consequential week of the project.

Integrations. Anything relying on someone else's system will take longer than planned, because their documentation is wrong somewhere and you will find out late.

The last 10%. Error states, empty states, permissions, edge cases, the admin nobody specified. This is routinely half the remaining time when a project "feels nearly done".

Why estimates slip

Not because developers are slow. Because scope grew, a decision waited three weeks for an answer, or an assumption made in month one turned out to be wrong in month three.

The fix is not a bigger buffer. It is shipping something small enough to be wrong about cheaply, then correcting.

What to ask for instead of a date

Ask for a working, deployable increment every two weeks. If you can open it and click it, the timeline is real. If you cannot see anything until month four, the timeline is a story.

Tell us what you are building and we will give you a range with the assumptions written down.