A system and method is disclosed for providing an improved voltage monitor that is capable of determining that a value of an adjustable supply voltage is suitable for a requested performance level in an adaptive voltage scaling system. An integrator circuit of the voltage monitor integrates a slack time error signal from a hardware performance monitor. Control circuitry evaluates a suitability of the integrated slack time error signal for the requested performance level for a number of voltage evaluation time periods. The adjustable supply voltage is deemed to be stable when the integrated slack time error signal is within a predetermined range of limits for at least two voltage evaluation time periods.