Methodology

The engine always follows the same steps. Every number it produces keeps a trace: the formula, the inputs and the parameters that gave it. That trace is what lets us answer "why this number?" for any line.

A price or a rate enters the cost database only with four facts: its source (price list, rental rate card, published wage, public specification), its date, its region and a confidence grade. On the site, these facts travel with every amount.

Prices are looked up from the most precise to the most general: the municipality, its market zone, its administrative region, then Quebec. When a region has no observed price, the province-wide value applies and the confidence grade drops one step.

A price ages. Aggregate or soil is considered current for 90 days, a rental rate for 30 days, delivery for 14 days, a manufacturer list or a disposal rate for 180 days. After that, the price is still used but flagged as stale.

Every value carries a grade from A to D. Anything graded C or D is labelled "estimate" in words, not only by colour. On the public site, results are always labelled "estimate": they are calculations, not quotes.

Every engine input has three documented values: low, typical and high (prices, waste, production rates, rental durations, disposal fees). The engine makes three deterministic passes. There is no random draw and no artificial intelligence.

Setting everything to its low, or everything to its high at the same time, stacks extremes that do not happen together on a real job. The displayed range therefore starts from the typical scenario and combines the effect of the main factors, measured one at a time, by the root of the sum of their squares. The result is rounded to two significant figures, so it shows no more precision than the data has. The three factors that move the total the most are named next to the result.

The range shows the effect of documented price and productivity spreads. It is not a probability.

There is no public source on how fast a do-it-yourselfer works in Quebec. The engine therefore starts from a professional crew's published production rate and multiplies it by a learning factor drawn from Wright's law, plus a share of rework. These factors are estimates (grade C) and will stay so until real data, aggregated over several projects, replaces them.

• Beginner: has never compacted a base or cut pavers.
• Intermediate: has done a similar project before.

The do-it-yourself cost counts materials at retail prices, rentals, delivery, disposal and taxes. Your time is counted separately, in hours and then in dollars (next section).

The hours of each guide step come from the same calculation as the total: each engine task is tied to the guide step that describes it, and the steps the engine does not calculate (planning, locate request, permits, checks) keep the guide's fixed time, added to the total. Calendar days count 8 h working days: person-hours divided by the number of people, then by 8, rounded up to the half day. Rain days and curing times come on top.

Doing it yourself costs money and time. The estimator counts both, for a beginner and for an intermediate do-it-yourselfer:

• Time cost: person-hours times the value of one hour.
• True cost: the money spent (materials, rentals, delivery, disposal) plus the time cost.
• Break-even: a contractor's typical price minus the money spent, divided by the person-hours.

If your time is worth more than the break-even, hiring costs less than doing it yourself. The amounts compared are before tax on both sides: GST and QST apply to both.

The value of one hour starts from the average hourly wage of all employees in Quebec, published by Statistics Canada. Replace it with yours: what you earn per hour, or what a free weekend is worth to you. The number of people does not change the time cost, only the number of days. Both values stay in your browser (local storage) for every estimator and project page; they are not sent to our servers.

The two words are often mixed up. A markup applies to cost; a margin is a share of the price. For the same percentage, a margin gives a higher price. The engine always shows which one it uses.

According to Revenu Québec, GST and QST both apply to the selling price before tax; QST is not charged on GST. The engine computes each on the same amount, rounds it to the cent, and shows them on two lines. A combined rate is never printed. The time you spend on your own work is not taxed; a contractor's whole invoice is.

• Formulas produce every number. Artificial intelligence never writes an amount, a quantity or a rate into an estimate.
• It can suggest: look up a price in a public list, summarize a source, flag a line that seems to be missing. Each suggestion comes with its evidence and waits for a person to approve it.
• Every call is logged, with a budget, and can be turned off.
• On the public site, no artificial intelligence runs while you read.

The engine has a version number, recorded with every saved project, so an estimate can be reproduced later. Guides show their review date and the next review due, along with a change log.

Known limits today: some items have no observed price yet and are listed separately, left out of the total; several product prices are industry estimates; do-it-yourself times are estimates; municipal rules cover only a few cities so far. Each of these limits is flagged where it applies.