I used to work for a large technology company which had the "we-only-match-if-you-contribute-each-pay-period" thing. Being engineers and being frugal and never one to miss an opportunity to optimize a solution, there were posts on internal message boards about how to contribute X% for the first Y pay periods, then Z% for the next W pay periods to optimize both hitting the IRS max and leave a minimum of employer contributions on the table. I don't remember all the details, but people spent a great deal of time doing the math. I think usually one could get to within about $50 of the theoretical best case.

Now I work for a company that trues things up, so I just max out around October or so and get true-up matches the rest of the year. I like it here better.

I don't understand. It doesn't seem hard to get it exact and leave nothing on the table.

If your salary changes during the year, it can mess with your % if you're trying to front-load as much as possible.

Hypothetical: $60,000 salary Jan-June, $65,000 salary July-Dec, contributions in whole percentage points 1-75%, match requires contributions in each twice-a-month pay period. $17,500/$60,000 = 0.29166. Contributions of 29% in pay periods 1-12 would be $725, or $8,700.

Then, when you get your raise, you're looking at contributions of $17,500-$8,700=$8,800 for the rest of the year. $8,800/[$65,000*.5]=0.27076. So you contribute 27% over pay periods 13-23, or $731.25 each, $8,043.75 total. For the last pay period, you've got $17,500-$8,700-$8,043.75=$756.25.

Then, for the last paycheck, set it to the max contribution percentage, but plan rules should max you out at the $756.25. So you've hit the match and max requirements with only 2 contribution changes. (Or 3 if you count going back down to 27% for the first period of the following year.)