On a variable price plan, the price per unit can change monthly, weekly or daily depending on market conditions or other factors. Consumers should look to specific offers for the terms of variability. The price per kWh or Mcf may vary from month to month based on the wholesale price of electricity and natural gas. You may be unable to predict the amount of your bill for electric usage because the price may change. While you may save money if the price decreases, you will pay more if prices increase.