How to use the number
Schedule that amount to leave on payday, into an account you do not spend from. If the figure is larger than a comfortable month, add months or shrink the goal. A number you will reverse is not the plan.
What this leaves out
Interest you might earn, fees, taxes, and weeks when pay is short. If your income changes, base the amount on a typical low month, not your best one. Irregular expenses, such as a yearly premium, belong in the goal itself or in the monthly picture on the savings plan.
This calculator is general education. It is not a forecast and not personal financial advice.