How the Pay Index is calculated

Every number on these pages traces to a public source, and every assumption is listed here. If a number can't be sourced, we show a dash — never an estimate dressed up as data.

Sources

Lodging & M&IE allowances — GSA FY2026 per diem master rates file (effective Oct 1). Where GSA lists seasonal rates for a destination, we average across seasons, because 13-week contracts start year-round.
Rents — Zillow Observed Rent Index (ZORI), ZIP-level, smoothed, all homes + multifamily. We take the median across a county's ZIP codes for the most recent month available and join it to the GSA destination's county.
Tax posture — state income tax structure (none / flat / graduated with top rate), shown as context only.

The formula

monthly lodging allowance = GSA nightly lodging × 30.4
13-week housing surplus = (monthly allowance − county median rent) × 3
13-week M&IE = GSA daily M&IE × 91

What this is NOT

Not take-home pay. Wages, hours, agency margins, and bill rates vary per contract and are not in this index.
Not your stipend. Agencies set stipends; GSA rates are the ceiling for tax-free treatment, not a guarantee.
Not tax advice. Tax-free stipend treatment depends on maintaining a tax home and other IRS rules.

Known limitations

ZORI measures asking rents — what landlords list, not what sitting tenants pay. Renewals at modest increases are under-represented, so ZORI can run higher than what a well-searched traveler actually pays. Your surplus may be better than shown.
Some GSA destinations span counties without ZORI coverage; those show a dash instead of a surplus.
Counties not specifically listed by GSA follow the standard CONUS rate ($110 lodging / $68 M&IE for FY2026) and are not individually ranked.

Update cadence

ZORI updates monthly (~16th); GSA rates annually in August, effective October 1. The index recomputes on both events, and the FY2027 changes page tracks the annual reset.