Methodology
How the number is arrived at.
This page exists so a price from BidParser can be defended. If a project manager, a client, or a bid protest asks where a figure came from, the answer should be a document, not a shrug.
Every adjusted price in the app also shows its own derivation, with the specific index values and multipliers applied to that item. This page is the general method behind it.
Source data
Two public sources: IDOT’s Pay Item Report with Awarded Prices from 2003 to the present, and ISTHA bid tabulations. Both are public records. New lettings are loaded within roughly a week of publication.
Only awarded prices enter a calculation. From 2023 IDOT publishes one row per bidder and marks the winner in a column. Treating every row as an award overstates recent prices by roughly a third on affected items — and recent prices are the ones weighted most heavily. Losing bids are retained as market data but are excluded from every average, percentile and confidence score.
- Awarded items
- 1,066,388
- Pay items
- 33,166
- Contracts
- 21,259
- Span
- 2003–2026
01 · Recency weighting
A flat average across 24 years is a history lesson, not a price. Each award is weighted by age before it enters the mean:
- 0–2 years
- 1.0
- 2–5 years
- 0.5
- 5–10 years
- 0.25
- 10+ years
- 0.1
Older awards are never discarded. They still shape the distribution a price is scored against, so a long history still tells you how volatile an item is — a 2007 award simply does not get an equal vote in what to bid this spring.
weighted avg = Σ(price × weight) ÷ Σ(weight)
02 · Inflation
Adjustment uses the Federal Highway Administration’s National Highway Construction Cost Index (NHCCI), quarterly, mapped to the IDOT division a pay item belongs to. Earthwork and structural steel have not moved at the same rate, and a single blended figure would hide exactly what matters.
Each award is adjusted by the ratio between the index in its own letting year and the index in your target year:
adjusted = nominal × (target index ÷ letting-year index)
There is therefore no single inflation factor for an item — there is one per award year. The app shows each of them.
Where no index exists for a division or a target year, adjustment is not applied and the app says so. A missing index quietly behaving as ×1.0 would be indistinguishable from a division whose prices genuinely have not moved, and those mean very different things.
03 · Region
Illinois is the baseline at 1.000. RSMeans-style multipliers cover all 50 states and DC, applied after inflation adjustment.
Be clear about what this is: a regional cost multiplier applied to Illinois award history. It is not award data from that state. For a job in Texas it is a reasoned adjustment, not an observation, and it should be treated with more caution than an Illinois number. Raw award data from other DOTs is on the roadmap.
04 · Confidence
Every price carries a percentile rank against the full historical distribution for that pay item, alongside p10, p25, median, p75 and p90.
A tight distribution over many recent awards is a number you can lean on. A handful of awards spread across an order of magnitude is a number that needs a phone call. The score exists to tell you which one you are looking at — not to make a single figure feel more certain than it is.
Worked example
Earth excavation, pay item 20200100, priced to 2026 in Illinois. These are the figures the app shows, and they reconcile:
| Weighted average, unadjusted | $53.80 |
| Inflation, NHCCI to 2026 index 310.8 | × 1.112 |
| Regional factor, Illinois baseline | × 1.000 |
| Weighted average, adjusted | $59.84 |
Drawn from 3,443 awarded prices, with eleven award years each adjusted by their own index ratio. The ×1.112 shown is the blended effect across that set.
Limits
The data is only as good as the source. It comes from IDOT and ISTHA as published. Where an agency publishes an error, republishes a correction, or omits a letting, the dataset reflects that.
History is not a forecast. This reports what contracts were awarded for. It does not predict what a future bid will cost, what you should bid, or whether a bid will win.
Unit prices carry context that a number cannot. A quantity of 2,000 cubic yards in Cook County and 400,000 downstate are different jobs. Every award shown carries its contract, county, district and letting date for that reason.
Outside Illinois is an adjustment. See section 03.
These are analytical aids, not engineering advice or a professional cost estimate. Verify before you rely on any of it — the bid is yours.
Something here look wrong?
Tell us which pay item and roughly which letting. A bad number is either a source error worth documenting or a bug worth fixing, and we would rather know which.