Formulas for estimating average incomes by fractile: (P = percentile)
| P90–100 = bi * P90 |
| P95–100 = bi * P95 |
| P99–100 = bi * P99 |
| P99.5–100 = bi * P99.5 |
| P99.9–100 = bi * P99.9 |
| P99.99–100 = bi * P99.99 |
| P90–95 = 2(P90–100) – (P95–100) |
| P95–99 = [5(P95–100) – (P99–100)]/4 |
| P99–99.5 = 2(P99–100) – (P99.5–100) |
| P99.5–99.9 = [5(P99.5–100) – (99.9–100)]/4 |
| P99.9–99.99 = [10(P99.9–100) – (P99.99–100)]/9 |
Source: Authors’ analysis of state-level tax data from Sommeiller 2006 extended to 2015 using state-level data from the Internal Revenue Service SOI Tax Stats (various years) and Piketty and Saez 2016