How estimates are built

Methodology

Every calculator combines public geographic indexes with HomeTrueCost base-price and scope assumptions. Public sources inform relative adjustments; they do not validate the final installed price.

Data snapshot 2026-09-12Manifest 494c74738ed47401live data

The pipeline

Labor

Assumed base labor dollars × a state/national employee wage ratio. HVAC uses SOC 49-9021; most other non-roof projects use construction-labor proxy SOC 47-2061. Wages are not contractor billing rates.

Materials

Base materials × your state's goods price level (BEA goods-RPP ÷ 100).

Permits

Assumed base allowance × a manually assigned state index. Added as a flat allowance; contingency still applies. Confirm your jurisdiction's actual fee.

04 → Total

( Labor + Materials ) × project size × scope factor × seasonal curve × quality tier + Permits, then × 1.10 contingency. Dollars are never multiplied by dollars-plus-indexes — only $ × dimensionless factors, then a flat 10% on top. Displayed labor, materials, and permits round to whole dollars; their sum is the subtotal, with rounded 10% contingency added.

((base_labor*wage_idx + base_mats*goodsRPP_idx) * seasonal * tier + permitBase*permitIdx) * 1.10

Worked example, live numbers

Roofing, Texas, mid-grade, medium pitch, June — computed right now from the current manifest, the same call the calculator makes:

Labor: $7,305
Materials: $6,619
Permits: $315
Subtotal: $14,239
Contingency (10%): $1,424
Total: $15,663

$12,750mid $15,663$18,600

Model sensitivity band $12,750–$18,600 — cross-market index spread, not quotes.

Sources

Source	Used for	Refresh
BEA Regional Price Parities 2024 (via FRED)	goods-RPP column / 100	annual Dec · free download
BLS OEWS May 2025 (Public API v2)	state/national annual-mean wage per SOC group (47-2181 roofers, 49-9021 HVAC, 47-2061 general proxy)	annual May · free, email-registered key raises quota
Zonda Cost vs Value	base-spec calibration boundary	annual Q1 · cite + link; no verbatim reproduction

Uncertainty bands

Every estimate shows a sensitivity band beside its point figure. It applies cross-state index differences to the model; it has not been calibrated against variation in local contractor bids.

Labor ± trade spread

roofers ±27.8%hvac ±22.4%general ±32.3%

Half the observed cross-state wage band, per trade.

Materials ±9.0%

Half the observed goods-RPP band, all states. Same figure for every project.

Permits flat · $50 outward

No range data, so permits don't move. Band ends round outward — the range can never exclude the mid.

What bands are not

Statistical confidence intervals
Bid guarantees
Intra-city precision

State averages cannot measure differences between cities or job sites. Contractor bids may fall outside the band. Base prices, tier/scope multipliers, seasonal curves, and permit indexes are assumptions rather than a survey of local prices.

Canada coverage

Pilot calculators under /ca/ run the same model in Canadian dollars against a separate manifest (last verified 2026-09-12, hash c156425586e8002a):

OntarioQuebecBritish ColumbiaAlbertaManitobaSaskatchewanNova ScotiaNew BrunswickNewfoundland and LabradorPEI + territories excluded — no wage data

✓ Province-priced

Wages

Job Bank NOC medians per province — roofers 73110, HVAC 72402, general labour 75110. Full differentiation, same as US states.

＝ National average

Materials

No provincial goods index exists in Canada. We ship the gap labeled rather than modeled — base specs converted at the 2025 Bank of Canada average (1.3978 CAD/USD), pending contractor recalibration.

Source	Used for	Refresh
Job Bank wages 2025 (NOC medians, ref 2023-2024)	provincial/national median per NOC group	annual Nov · free bulk CSV, Open Government Licence
Bank of Canada FXUSDCAD 2025 average	USD→CAD base conversion (pending contractor recalibration)	annual · free Valet API
Zonda Cost vs Value	base-spec calibration boundary	annual Q1 · cite + link; no verbatim reproduction

Try the Canadian roofing calculator

Limitations

Estimates, not advice

Planning figures from public data — never professional guidance, never a bid.

Permits vary by city

A state-indexed allowance is shown, not a quote. Confirm exact fees with your city.

Annual data lags shocks

Material spikes trail yearly BEA/BLS releases; the quarterly index and crowdsourced actuals recalibrate drift.

Model calibration

Wages and goods-RPP adjust a calibrated base spec; they are not contractor quotes or a substitute for local bids.