Start by working out what is missing. A savings goal should start from the money you have already set aside for it and the number of contributions left.
An example with numbers
You want $6,000 in 18 months and already have $1,500. With no return, $4,500 is missing. Split over 18 contributions, you need $250 a month. Starting from zero, you would ask yourself for about $333.
Try it with your numbers
Choose “How much to save each month”, enter your current savings and leave the return at zero. Then change the time frame to find a contribution you can manage.
Example figures for learning purposes. They are not a recommendation and do not replace professional advice.