This study identifies monetary and fiscal policy regimes in Iran, and the resulting policy mix, over 1975–2024, the longest period with jointly available data. Monetary policy is a base-money growth rule responding to the inflation gap; fiscal policy is an operating budget balance rule responding to lagged government debt to the central bank, controlling for oil revenue, the output gap and COVID-19. Each rule is a Markov-switching regression with switching intercept, policy coefficient and error variance, estimated by penalized maximum likelihood to exclude degenerate regimes. The number of regimes is selected by sequential parametric-bootstrap likelihood-ratio tests, and time-varying transition probabilities driven by sanctions, war, oil shocks, exchange-rate depreciation and financial repression are tested against constant ones. The data select two monetary and three fiscal regimes. Monetary policy is passive throughout: base-money growth either ignores inflation (coefficient −0.09, in oil-boom years) or accommodates it (0.64). Fiscal policy cycles from a strongly passive regime (debt coefficient 0.11) to a weakly passive regime (0.04) and then an active regime in which deficits widen as debt rises (−0.03). The policy mix is therefore indeterminate in 35 of 50 years and fiscally dominant in 15 (1975–1977, 1986–1988, 2015–2023), when inflation averaged 28.6 percent versus 19.3 percent under indeterminacy; monetary dominance never occurs. Sanctions, war, oil shocks and exchange-rate depreciation do not affect transition probabilities. The active fiscal regime coincides with deep financial repression, but the real deposit rate’s effect on transitions is insignificant under a parametric bootstrap (p = 0.15). The passive monetary stance and active fiscal regime are robust across 21 alternative specifications, and the regime-switching rules forecast 2019–2024 as accurately as linear rules. Price stability requires an enforceable fiscal rule, removal of financial repression and a monetary instrument that can lean against inflation.