changing percentages equal across 12 months

I am working on a budget. We are budgeting the amount of money that we are going to place into savings each month based on the amount of sales that are budgeted each month. So if we are placing $100,000 a year into savings we will place a different percentage of that $100,000 each month. I want to adjust the dollar amount for one or two months and have the percentages change accordingly or at least the remaining months dollars change so that I still come up with $100,000 at the end of the year.
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