Methodology
This page is the reason the site exists. If a number appears in a CostCandor calculator, this page tells you where it came from, what we assumed, and when it was last checked.
The contract every calculator follows
- Published formula. The exact arithmetic is printed on the calculator page and restated here. No black boxes.
- Sourced inputs. Every price table carries a
sourceand anasOfdate in our data files. If we can't document an input, we don't ship the tool. - Ranges, not point estimates. Real projects vary by region, access, and condition, so we always publish a low / typical / high band.
- Regression tests. Every calculation function has automated tests with hand-computed expected values that run before any deploy. A formula change that shifts results must change the tests, visibly.
- Review stamps. Calculators and guides display a "last reviewed" date plus the pricing data's as-of date.
Where the price data comes from
Our roofing tables are seeded from three classes of sources, cross-checked against each other:
| Source class | What we take from it | Cadence |
|---|---|---|
| U.S. BLS Producer Price Index — roofing contractors (PCU238160238160) | Direction and magnitude of installed-cost changes over time | Checked quarterly |
| National retail shelf pricing (Home Depot, Lowe's) | Material floor prices: shingles, underlayment, flashing, fasteners | Checked quarterly |
| Published contractor cost surveys (2025–2026 editions) | Installed cost per square including labor, and regional spread | Annual editions |
Current roofing dataset: as of 2026-06. Seed values are our documented starting estimates; each scheduled refresh replaces them with a logged price pull and updates the as-of date shown on the calculator.
The roof replacement formula, in full
roof area = footprint × pitch factor(1.02 flat · 1.08 low · 1.20 medium · 1.42 steep)
squares = roof area ÷ 100
band cost = squares × 1.10 waste × material $/square(band) + squares × tear-off $/square(band)
The pitch factors are standard geometric slope multipliers used in roofing takeoffs; the 10% waste factor is the industry's conventional allowance for simple-to-moderate roofs. Both are assumptions you can disagree with — which is exactly why they're printed.
What we deliberately don't do
- We don't collect your address, email, or phone number to show results, and we never sell leads to contractors.
- We don't publish a tool whose data pull isn't documented on this page.
- We don't present a single-number "your cost" figure. Any site that does is guessing with confidence.
Corrections
Found a stale price or a formula error? Email us via the contact page. Corrections ship with a visible change to the review stamp on the affected page.