IF formula for budget purposes

Hello all,

I am setting up a personal budget spreadsheet to track my monthly income and expenses and there are a couple of dynamic features I would like to add, if possible.

First, under each category (Housing, Transportation, etc), I have 2 columns; 1 for actual expenditures, 1 for my budget limit for each item for that month. I would like to set up a formula that affects the actual expenditure column in relation to the budget limit column. For instance, under Transportation, I am budgeting $50 per month for taxis. When the actual expenditure for taxis is between 0-90% of that $50 budget (so, $0-45), I would like the cell to be green. When the actual expenditure is between 91-100%, I would like the cell to turn yellow. And, when the actual expenditure goes over my monthly budget, I would like the cell to turn red.

Second, I would like the monthly spreadsheets to work with one other. I would like the difference between the actual expenditure for an item and its budget to roll over to the next month's budget for the same item. So, say I budget $20 every month for gifts. If I spend $10 on gifts in June, I'd like the budget for gifts in July to bump up to $30, to include the $10 that wasn't spent in June. Conversely, if I overspend on gifts, say $30 in June, I'd like that to affect the following month's budget, so that July would be $10.

If anybody can help with either or both, I'd greatly appreciate it. Also, if anyone knows of another thread or two that offer really useful tips for building out a dynamic budget with great features, I'd love to be put onto that as well.

Thanks in advance for your help,
Brett