Do you use EA's story progression, or do you run a modded one, specifically NRaas story progression? If so, do any of your sims in the active household have a baby, toddler, child, or teen that doesn't live in the active household? Or did you move out any elder parents? The amount being subtracted is similar to what child support or elder support payments are if you run that mod. I believe it deducts twice a sim week.