You want to get a list of contacts by subtracting from a date or numeric field type value in a database.
To subtract from a date field type within a classic query, the negative number must be outside the brackets.
For example, this is how to set up date subtraction query criteria: [PurchaseDate] greater than [Last Modified Date]-5.
The same can be done for numeric field types. For example, [PurchaseAmount] greater than [PreviousPurchaseAmount]-2