My wife is currently putting $15,000.00 per year in her 403b. Assuming an average 6% - 7% per year gain for the next 10 years and assuming taxes will rise significantly (who knows how much) I'm wondering if it still makes sense to be putting money into a tax deferred account. If I'm in a 28% tax bracket now and that goes to 35% by the time I withdraw the money did I really accomplish anything by deferring?
I'll let others talk about whether your numbers are correct, I'll just give you my idea of the math.
If you go the 403b route, you'll take $15,000 of pre-tax money and put it into an account that accumulates at 6% a year for 10 years. You will have $26,863 in the account then. If you withdraw it and pay 35% tax, you'll have $17,461 of spendable cash.
If you go the taxable route, you'll put $10,800 of after-tax money in an account. If the account grosses 6% every year, but you pay 28% annually on the gain, you will be accumulating at 4.32%. After 10 years, you'll have $16,485 of spendable cash.
The 403b is the better strategy with these assumptions.
Note that your tax rate will probably go up sometime during the 10 years. If it's 35% in some of the "later" years, your accumulation in the taxable account for those years is only 3.9%, and the 403b advantage is bigger.
Also, note that the taxable strategy is better if you are holding the money for only a "few" years, but long enough for your marginal tax rate to go up. The cross-over point is somewhere between 5 and 7 years, depending on when the shift to 35% occurs.
OTOH, if you use the "taxable" strategy, but put the entire $10,800 in non-dividend paying stocks, which earn 6%, you'll have $19,341 in the account at 10 years. If you sell the stocks and pay a 15% LTCG rate on the gain, you end up with $18,060 of spendable cash. This strategy is best for any period that is long enough to qualify for the 15% rate.
[caveat - I made a stupid error on something that wasn't any more complicated than this a couple days ago, so take my comments as a "second opinion" that you can compare to your calculations.]