When most mortgage lenders calculate escrows/reserves required at closing they look for 14 months of reserves. The key in figuring how many months will be collected at closing will depend on when the first mortgage payment will be due, the renewal dates of their insurance policy, and when the taxes, if any, are due.
Example: The closing date is January 31st with a first payment due March 1st. Taxes are due December 31st. Homeowners insurance premiums are due July 11th.
Taxes: How many payments would they make before the taxes would be due? They would pay into their escrow account March, April, Many, June, July, August, September, October, November, December for a total of 9 months. Remember, we are looking for a total of 14 months so you would subtract the 9 months that they paid into the escrow account from the desired 14 months and that would leave 5 months being collected at closing.
Homeowners Insurance: How many payments would they make before the premium would be due? They would pay into their escrow account March, April, May, June, July for a total of 5 months. Subtract the 5 months that they paid into the escrow account from the desired 14 months and that would leave 9 months being collected at closing.
You can figure the aggregate adjustment once you have the annual insurance premiums, taxes, etc. and have figured how many months will be collected at closing. Once you have the initial escrow account disclose statement, take the initial deposit and subtract that figure from the amount of reserves that will be collected at closing and the difference will be your aggregate adjustment.
Example: You have determined that at closing we will collect 3 months of taxes for a total of $112.86 and 3 months of hazard for a total of $153 which equals $265.86 and the initial deposit on the initial escrow account disclose is $177.24, you would take the $265.86 minus $177.24 and that equals $88.62. So your aggregate would be -$88.62.
Keep in mind this may not be exactly how all lenders handle this, but it will help you get a good idea of how to calculate your reserves and the aggregate that will be required at closing. Hopefully, this will help you figure your expenses where last-minute surprises will not come up at closing due to inaccurate escrow calculations.
I find escrow calculations on good faith estimates to be one of the biggest problems that result in "at closing shockers". I have heard many stories from closing attorneys and real estate agents regarding this issue. We need to take a few seconds extra to make certain that the figures we give our clients are truly as accurate as possible. If there are issues that arise during the lending process that would cause those figures to become invalid, re-disclosure of terms is necessary. This truly can be the difference between a smooth transaction and a nightmare.