I am trying to customize a report (Contribute/Summary) to compute LAST YEAR "to date" totals (so I can compare them with how we are doing so far this year). I have created the new template/php files but am at a loss where to "subtract the one year" from the "current year-to-date field" before the query is done. Any pointers would be greatly appreciated. Thanks!
You may want to first check out the Advanced Fundraising Reports extension before you go too far down that road - I think it has the option you want.
Second - I've been working on user-configurable date filters - I'm hoping to get them into the next version of Civi, so you don't have to modify code to get a new filter.
Third - since you need this now and not later - you'll want to override one or both of these core files: CRM/Core/Form/Date.php CRM/Utils/Date.php (function relativeToAbsolute).