Retrospective Tax Enforcement and Perceived Revenue-Generation Effectiveness of Back-Duty Audits in Southwest Nigeria

This study isolates the role of back-duty audit as a retrospective enforcement mechanism for revenue recovery in Southwest Nigeria. It draws on a 2025 survey of 374 employees of federal and state revenue authorities across Lagos, Ogun, Ondo, Osun, Oyo and Ekiti States. Still, it develops a scope distinct from broader tax-audit analyses by focusing on historical non-compliance, random and regular retrospective assessment, and the recovery implications of deeper audit intensity. Item-level descriptive statistics show the strongest support for organising random back-duty assessments (mean = 3.2326, SD = .8425) and regular assessments (mean = 3.0963, SD = .8390), while auditing doubtful exclusion from the tax base receives the lowest mean (2.4759, SD = 1.1500). Back-duty audit has the largest bivariate association with reported revenue generation among the three audit modes (r = .373, p < .001). In a multiple regression controlling for desk and field audits, it remains the dominant predictor (B = .313, SE = .046, standardised beta = .346, t = 6.839, p < .001). The internally reconciled overall model is significant, F(3, 370) = 23.125, p < .001, with R² = .158 and adjusted R² = .151. The paper interprets back-duty audit as a revenue-recovery mechanism with a plausible deterrence role rather than merely an exercise in historical correction. Consistent with recent evidence on audit scope, compliance-risk management and digital enforcement, retrospective audits are expected to be more effective when they are risk-targeted, sufficiently comprehensive, linked to collection processes and supported by integrated information systems (Kotsogiannis et al., 2024; OECD, 2024; OECD et al., 2025). These findings have particular relevance to Nigeria’s current tax-reform transition. The Nigeria Tax Administration Act 2025 commenced on 26 June 2025 and establishes uniform procedures intended to facilitate tax compliance and optimise tax revenue, while the Federal Ministry of Finance’s 2026 transition guidelines address the movement from the repealed tax laws to the new tax framework from 1 January 2026 (Federal Republic of Nigeria, 2025; Federal Ministry of Finance, 2026).