Problem: Suppose you earn $120,000 a year and plan to contribute the $11,000 maximum to your 401(k). Either because you're overcontributing or because you got a bonus that you hadn't planned on, you've already put $8,000 in the plan. It looks as if you'll max out in October and miss two months of the company's match. You need to readjust your contribution rate.
$3,000 (maximum minus year-to-date contribution)
5 (Number of months left in the year) = $600 per month
Solution: Reduce your monthly 401(k) contribution to $600, or 6% of pay, to get the plan back on track.