Are firms sophisticated maximizers, or do they appear to make mistakes? Using transaction data from Ugandan value-added tax returns, we show that sellers and buyers report different amounts 79% of the time, despite invoices being easily cross-checked. Our estimates suggest that most firms are “advantageous misreporters,” but that 25% are “disadvantageous misreporters” who systematically overreport own sales minus purchases such that their tax liability increases. Similarly, many firms—especially disadvantageous misreporters—fail to VAT-report imported inputs they themselves reported at Customs, increasing their liability. On net, unilateral VAT misreporting cost Uganda about US$384 million in foregone 2013–2016 tax revenue.

Using administrative tax records for U.K. businesses, we document both bunching in annual turnover below the VAT registration threshold and persistent voluntary registration by almost half of the firms below the threshold. We develop a conceptual framework that can simultaneously explain these two apparently conflicting facts. The framework also predicts that higher intermediate input shares, lower product-market competition, and a lower share of business to consumer sales lead to voluntary registration. The predictions are exactly the opposite for bunching. We test the theory using linked VAT and corporation tax records from 2004 to 2014, finding empirical support for these predictions.