Systems and methods for a method for determining a critical effective k at an off-rated core state of a nuclear power plant includes determining, for the off-rated core state a control rod density, a percent core power, a gadolinium reactivity worth, a doppler reactivity worth, and a xenon reactivity worth responsive to a control rod pattern, a reactor power plan including the off-rated core state, and a reference effective k, calculating a change in an effective k from the reference effective k at the off-rated core state responsive to two or more parameters selected from the group consisting of the control rod density, the percent core power, the gadolinium reactivity worth, the doppler reactivity worth, and the xenon reactivity worth, and generating the critical effective k for the off-rated core state responsive to the change in the effective k from the reference effective k.