Define the goal
Use a specific target rather than 'save more' when the amount can be estimated.
Subtract what is already saved
Only the remaining gap needs to be funded.
Divide by time
A simple contribution amount can be calculated from the gap and number of periods.
Adjust one variable
If the monthly amount is unrealistic, change the date, target amount or other spending assumptions rather than hiding the gap.
Educational information only. Use current product terms and the rules that apply in your country. For decisions with significant financial consequences, consider an appropriately qualified professional.