Need a formula that subtracts or adds a a specific value

I have a workbook where that deals with weights. I need a formula that will subtract the extra weight taken from it. for instance if i move 5050 lbs and the goal was 5000 then i just want to subtract the 50 extra pounds. also i want to be able to add weight tot the next cell if i don't achieve the goal of 5000.

That doesn't make much sense to me. Can you re-phrase it and/or attach a sample workbook. Make sure there is just enough data to make it clear what is needed. Include a BEFORE sheet and an AFTER sheet in the workbook if needed to show the process you're trying to complete or automate. Make sure your desired results are demonstrated, mock them up manually if needed. Remember to desensitize the data.

Pete