There's no way that number is correct. You're only allowed to save $18,500 in your 401(k) for 2018. You'd hit that number in less than 3 months.

I'm guessing that you must be closer to retirement age right now and probably haven't saved enough or had investments with low returns (no personal judgement here, shit happens). Thus the system is predicting how much "catching up" you need to do and not taking various parameters such as your age and the laws in to account.