Building your first calculator template

Every quote in Karven runs through a calculator template. The template is a small JSON document that knows the inputs a job needs, the formulas that price them, and the line items that end up on the PDF. You don't have to write JSON to use Karven, every supported trade ships with a polished default, but you can override almost any number from the UI in Settings → Calculator.

The mental model

Three things make up a template:

1. Onboarding answers. "Tell me about your shop." Asked once, then re-used on every quote. Example: which decking species you usually quote.
2. Job inputs. "Tell me about this specific job." Asked per quote. Example: deck width × length.
3. Formulas. "Given the answers, here's the price." The engine evaluates these in order. Later formulas can reference earlier ones.

The PDF is just a render of the output of step 3. There is no separate "PDF template" you maintain.

Three calculator patterns

Karven supports three template shapes. Most trades fit one of them cleanly:

• Configurator. You pick from a small list of options and the price comes from a lookup table. Example: garage doors. The customer wants a 2.4m × 5.0m sectional with a B&D Controll-a-door 4, in Surfmist. Price is determined by panel dimension, motor model, and colour.
• Volumetric. You measure the job in m², m³, or linear metres, and multiply by a rate. Example: concreting. 60 m² of 100mm slab at $X/m² + pump hire + saw cuts.
• Flat-rate. Job size doesn't really vary. You quote per call-out or per job. Example: a service trade doing a fixed-fee inspection.

Picking the wrong pattern is fine, you'll just end up with extra inputs on your screen that you ignore. Picking the right one means the calculator stays out of your way.

Editing a template (no JSON)

Settings → Calculator → Edit defaults.

You'll see your active template grouped into sections:

• Materials: unit prices for everything that goes into a job. Joist timber, fixings, concrete, paint, whatever.
• Labour: hourly or daily rates, plus a list of operations with their default duration.
• Markup: applied to materials, labour, or both. See material markup explained.
• Overheads: fixed costs added per quote (yard hire, insurance prorate, fuel).

You change a number, hit save, and the next quote you build uses the new value. Existing draft quotes keep the old number unless you explicitly recalc them.

Adding a custom line item

If you regularly add a fee that isn't in the default, say, a "remote storage delivery" charge, add it as a custom add-on:

Settings → Calculator → Add-ons → New.

Fields:

• Name (shows on the PDF)
• Default amount
• "Always include" or "Optional toggle on each quote"
• Taxable (yes/no, defaults to your GST setting)

The add-on then shows up as a checkbox or pre-filled line on every new quote.

Override on a single quote

Sometimes you want to change a number for one job only, not for every job. Inside the quote, click any line item amount. A small inline editor opens. Change the number, write a one-line note (the engine asks for one so you know later why this quote is different), save.

The note appears in the audit log on that quote. It doesn't appear on the customer PDF.

Where the defaults come from

Each trade's defaults are built from the supplier price feeds Karven ingests weekly, plus a moderation pass to make sure regional pricing is sensible. They're typically within ±5% of what an experienced tradie in that region would quote.

You can see when the defaults were last refreshed at the top of the calculator settings page. If they're more than 60 days stale, Karven nudges you to review them.

What not to override

Don't override the engine's internal formulas, the ones that compute things like "joists per metre of deck width given joist spacing". These are pure maths. If you find yourself wanting to override one, that's usually a sign you're trying to express a different rule of thumb (e.g. you use 450mm spacing instead of 400mm), change the onboarding answer instead.

Versioning

Karven keeps every saved version of your calculator. Settings → Calculator → History shows the diff between any two versions. If you accidentally clobber a rate, roll back in one click. Quotes that were sent under an older version reference the version they were built with, so you can always reproduce the original maths.