Cost Drift

How far each project's budget has moved from its original commitment.

What it shows

Three tabs:

  1. By absolute change — biggest dollar blowouts first. This is where the Big Build mega-projects dominate.
  2. By percentage — biggest relative blowouts first. This surfaces smaller projects whose budgets have tripled or quadrupled.
  3. Decreased — projects whose TEI actually fell. The rare good-news list.

Each row includes a sparkline showing the TEI trajectory across every Budget Paper 4 release we hold.

How to read it

  • Absolute change = current_TEI - original_TEI, in dollars.
  • Percentage change = (current_TEI - original_TEI) / original_TEI * 100.
  • The sparkline is not smoothed — each point is an annual BP4 snapshot.
  • A flat sparkline means the project's TEI hasn't moved since its first listing (which may be suspicious for a long-running project; governments sometimes stop updating TEIs for politically sensitive projects).

Data sources

  • Time-series TEI records from Budget Paper 4 releases we have ingested (currently covering 2023–24, 2024–25, 2025–26, with earlier snapshots where available).
  • The TEISnapshot model holds every historical value with publication date.

Caveats

  • A big absolute blowout on a $20bn project may be proportionally small. Use the percentage tab as a sanity check.
  • A big percentage blowout on a $50m project may still be trivial. Look at both tabs.
  • Cost drift doesn't capture scope changes — a project can absorb a blowout by quietly removing features. See Project Detail for scope change logs.

Last reviewed: 11 Apr 2026