The parts, running, so you can point at the ones you need.

The five things that drive it

RRecords

How many different kinds of thing does the system have to hold? Customers, jobs, invoices and materials are four kinds. Two hundred customers is not two hundred kinds, it is one, and that difference is the single most common misunderstanding we have to unpick on a first call.

OOutside

How many systems does it have to talk to that we do not control? Your accounting package, a card processor, whatever actually sends the email. Each one is somebody else’s software with its own login, its own limits and its own release schedule.

CConsequence

Is money or somebody’s identity involved? A tool that shows the wrong total is embarrassing and fixable in an afternoon. A tool that shows one customer another customer’s invoice is the kind of thing that ends a relationship, so that code gets written more slowly and checked more times, and you are paying for the checking.

SSurfaces

How many places does the same information have to appear? A list on a laptop, a chart, a printed sheet and a phone in a truck are four surfaces, and each has its own idea of what counts as the same information.

MMess

How much of what you already have has to come across? A spreadsheet somebody has kept tidy moves over without much drama. Eleven years of one, with merged cells and a tab called do not use, does not, and nobody can tell you which of the two you have until the file is open.

The three rules that bend the arithmetic

1. The first one is the expensive one.

   The first table in a system settles how information is stored, how it is loaded, how it is edited and what happens when two people change the same row at once. Everything after it inherits all of that. So within a family, the first couple of things you tick count in full and the rest count as variations on work that has already been paid for.

2. Things we do not control never get cheaper.

   Every outside system is its own separate unknown. Its documentation is a version behind, it has an opinion about how often you may ask it questions, and it changes on a Tuesday without telling anybody. The second one is not easier than the first, because it belongs to a different company. These do not discount, and a build with three of them in it is a different animal from a build with one.

3. Money and identity are about care, not code.

   Payments, logins and permissions are not more lines of code than a list is. They are more care — more thought about what happens when something half-works, more checking, more attention to the edge case that turns up once a year. The care is the cost, and it is the thing we will not trim to hit a number.

Where a selection lands

Four possible answers, and they are the same bands published on the front page. There is nothing here that has not already been committed to in public.

• from $900

  A small job

  Everything you ticked is a variation on something else in the same family, nothing has to talk to a system we do not control, and no money or login is involved.

• $1,500–$3,500

  An ordinary project

  The common case, and where most of this work lands. One demanding piece, or several ordinary ones, and at most a couple of outside systems.

• No figure

  A larger engagement

  Two or more demanding pieces, or three or more outside systems, or money and logins and roles all at once. These are quoted exactly the same way: fixed scope, fixed price, agreed in writing before work starts. They are quoted from a conversation rather than from a list.

• No band at all

  Needs a conversation

  Some things cannot be priced off a list, and when you tick one the page says so rather than guessing. Working offline on a phone with no signal is the usual example. It still goes in your brief, because the brief describes the job rather than filtering it.

One property of those four is worth knowing before you start ticking. Adding parts can move you up a band, or out of banding altogether, and nothing you can do moves you the other way. You cannot game it, which is mostly a protection against arriving at a call believing you have.

And if it comes out bigger than you hoped

Then the page proposes a first phase instead of shrugging at you, and here is the rule it uses so you can check its work. A first phase is the foundations — how information gets in, where it lives, and who is allowed to see it — plus the single most valuable thing you would do with it. Everything else becomes a second project, and it is genuinely cheaper by then, because the first one paid for the floor it stands on. Knowing what to build first is the skill most people hiring a developer have never had a reason to learn, and it is worth more to you than the estimate is.

The method, worked through on a real shape of job

A shop that quotes work in a spreadsheet and wants the quote, the job and the invoice to live in one place. We have built versions of this more than once. Here is what the five drivers say about it.

What you picked, and what it means.

Choosing parts needs JavaScript, which is switched off in this browser. The catalogue above is the complete list either way, and the worked example under How the price is worked out shows what this section does with a selection.