Depends on what tax bracket you're in and what the fee difference is. There is no generic piece of information that will fit your particular circumstance.

This is a math problem for the most part. Figure out your tax savings if you maxed your 401k. Figure out what the fees would be on that maxed amount. If your tax savings are greater than your fees then the 401k is a better choice.

Just checked 2012 tax file, we're in the 25% bracket. From checking online, it looks like we were $4K above the line. I'm not sure how much difference there will be between this year and last year. Assuming not much difference from last year to this year, all we would need to do is get $4K (roughly) into her 401K before April 15 this year to get us into the next lower tax bracket?

Is there another way to figure out how much we need to put in to her 401K besides doing our taxes to figure out what our Taxable Income is (after deductions, etc...)? Or just do them, don't file, put the money into the 401K, and redo them?

Are you familiar with marginal tax rates? Just based on your post, it sounds like you aren't thinking through the tax situation as clearly as you could.

As a basic run-down, you pay the tax rate at each income level for each dollar up until the top of that income level. For an example, a single person making $50,000 in 2013 would pay the following amounts in these

tax brackets:10% of the first $8,925 or $892.5

15% of anything between $8925 and 36,250 or .15*(36,250 - 8,925) or 4,098.75

25% of anything between $36,250 and $50,000 or .25*(50,000-36,250) or 3437.5

The total would be 892.5 + 4098.75+3437.5 = 8,428.75. That averages to a 16.8% tax rate, but the marginal rate is 25%

In your case, I'm assuming you're married with AGI of $76,500? By reducing your taxable income to $72,500, you're saving $4,000*your marginal tax rate or $4,000*.25 = $1,000. By reducing it another $4,000 to $68,500, you save an additional $4,000*.15 = $600.

Again, when I use the word save, it really means save now, and you'll potentially pay more later. But you'd only pay more later if you expect your future marginal tax rate on the $4,000 to be higher than 25%.

Let me know if you need clarification on anything I wrote.