Premorbid IQ estimates are used to determine decline in cognitive functioning following trauma or illness. This study aimed to: 1) further validate the New Zealand Adult Reading Test (NZART) in a New Zealand population and compare its performance to the UK developed National Adult Reading Test, and 2) develop regression formulae for the NZART to estimate Wechsler Adult Intelligence Scale-IV (WAIS–IV) IQ scores. The 67 participants (53 females; 16 Māori), aged 16 to 90 years old (mean age = 46.07, SD 23.21) completed the WASI-IV, the NART and the NZART. The NZART predicted Verbal Comprehension Index (VCI) scores slightly better than the NART (r =.63 vs. r = .62) and explained 33% of the variance in FSIQ scores. Reasons for developing regression formulae for the NZART are discussed, regression formulas for the NZART based on the WAIS–IV are included and suggestions of alternate ways of determining premorbid IQ are made.