Let me answer

@542thruNthru question.

Say you made $1,000 each week and you contributed 10% to 401K; that would be $100 each week. Now if you got a $100 raise, your check would now be $1,100 each week, minus 10% to 401K which is now $110. So, you are only giving $10 of your $100 raise to your 401K. Your check would be $90 more each week and you would certainly spend it each week.

On the other hand, if when you get your $100 raise, you were to raise your contribution to say 15%. That would amount to $165 (15% of $1,100 = $165) towards your 401K each week. So, your check would be $35 more each week than what you were used to before the raise; and your 401K would see $65 more each week.

So, by doing nothing, you only contribute $10 more to your 401K. But by changing your contribution %, your contribute $65 more. And if you do that at a time when you get a raise, you don’t feel the increase to 401K because it was money you weren’t used to making before the raise; and the cherry on top is that you would still see a $35 raise on each check take home pay.