A method for HVAC workload and cost logic is described. In one embodiment, the method includes detecting a thermostat of an HVAC system being set to a target temperature and upon detecting the thermostat being set to the target temperature, detecting a current indoor condition and a current outdoor condition. In some embodiments, the method includes calculating an estimated runtime of an HVAC heating or cooling cycle for the target temperature. The estimated runtime is based on the target temperature, the current indoor and outdoor conditions, and on a result of querying a correlation database. The correlation database includes data points for a plurality of previous HVAC heating and cooling cycles.