We're told the computations are complicated, because Lindsay has had so many cases. But based on the 120 day suspended sentence for shoplifting, time served under house arrest, and her prior DUIs, Lindsay could be thrown in jail for a long, long time.

We've learned Lindsay MUST be in court Wednesday to face the judge ... and the judge has lots of questions, including why Lindsay was a no-show 9 times at the Downtown Women's Center, where she was performing her community service. And the judge will almost certainly want to know why Lindsay didn't comply with the order to spend a minimum of 4 hours at a time when she showed up at the Women's Center.

TMZ broke the story, Lindsay was booted from the Women's Center because of all the problems and reassigned to the American Red Cross.

And one more thing. The judge will almost certainly ask Lindsay why she didn't meet with her shrink every Monday for 1 hour, as required by court order. Lindsay claims she did a bunch of therapy sessions by phone.