How to calculate tax amounts withheld on mixed pre-tax and Roth 401(k) contributions, and match?
When you adjust your investments the following will happen: Initial condition: Modified condition: This means that after this change you will note that the amount of federal tax you pay each month via withholding will go up. You are now contributing less pre-tax, so your taxable income has increased. If you make no other changes, then in April you will either have increased your refund by 6 months x the additional $25 a month, or decreased the amount you owe by the same amount. There is no change in the total 401K balance at the end of the year, other than accounting for how much is held pre-tax vs. Roth post-tax. Keep in mind that employer contributions must be pre-tax. The company could never guess what your tax situation is. They withhold money for taxes based on the form you fill out, but they have no idea of your family's tax situation. If you fail to have enough withheld, you pay the penalty — not the company. *The tax savings are complex because it depends on marital status, your other pre-tax amounts for medical, and how much income your spouse makes, plus your other income and deductions. Its easier than that: employer matching contributions are  always pre-tax. While your contribution is split between the pre-tax and the Roth post-tax parts, matching contributions are always pre-tax. Quote from the regulations I linked to: For example, matching contributions are not permitted to be allocated to a designated Roth account. So the tax you pay is only on the Roth portion of your contribution. One of the reasons for that is the complexity you're talking about, but not only. Matching is not always vested, and it would be hard to determine what portion to tax and at what rate if matching would be allowed to go to Roth. Your 401k IRA will now have three different sub-accounts, the one holding your Traditional (pre-tax) 401k contributions, the one holding your Roth 401k contributions, and the one holding the employer match contributions (which, as has been pointed out to you, cannot be considered to be Roth 401k contributions). That is, it is not true that So my next month's check shows $500+$500 going to the regular 401k, and $82+$82 going to the Roth 401k. Your next month's paystub will show $500 going into the regular 401k, $100 going into the Roth 401k, and if employer matching contributions are listed on the paystub, it will still show $600 going into the employer match. If you have chosen to invest your 401k in mutual funds (or stocks), shares are purchased when the 401k administrator receives the money and are also segregated in the three subaccounts. If you are paid monthly, then you will know on a month-by-month basis how many shares you hold in the three  separate subaccounts, and there is no end-of-year modification of how many shares were purchased with Roth 401k contributions versus how many were purchased with  pretax contributions or with employer matching funds as you seem to think.
Ok. I'll ask - Does the job offer a 401(k)? Matching deposits? You see, the answers given depend on your risk tolerance. There are two schools of thought, one extreme will tell you not to start investing until you have the emergency fund set up, the other, start from day one. I accept there are pros and cons to either approach.  But - if you have access to a matched 401(k), even a conservative, risk-adverse approach might agree that a 100% match (on the first say 5% of your income) is preferable to saving in a low return emergency fund. If the emergency occurs, a low interest loan for the need is a cheap way out. Since the money goes in pre-tax and is matched, being able to borrow out half (IRS rules) effectively lets you borrow more than you deposited out of pocket. And the word emergency implies a low occurrence event. Deposit to the match and start the emergency fund in another account.  If no matched 401(k) at work, the other two answers are great.  Edit - To clarify, and answer a comment below - say the risk isn't just a money emergency, but job loss. $1000 deposited to the 401(k) cost $850 out of pocket, assuming 15% bracket. After the match, it's $2000. After the job loss, if this is withdrawn, if the 15% still applies (it may be 10% or even 0%) the net is $1700 less the 10% penalty, or $1500 back in your pocket.  There are those who will say they are just not comfortable running an emergency account so lean, I understand that. For the OP here, $800/mo is nearly $10,000 per year. If even half of that can be deposited pre-tax and matched, the account will grow very quickly and there would still be cash on the side. tl;dr: Please please please do the conversion first. JoeTaxpayer's answer is correct, but I am of the opposite opinion. First, there's just about no reason to have post-tax dollars in a Traditional IRA.  You'll eventually have to pay tax on the earnings those dollars generate, so it's essentially the same as having that money in a regular taxable account.  Meanwhile, if you roll those dollars into a Roth IRA, you get to earn tax-free money on them for the rest of your life (and even after your death)! Second, even if you did have some reason for keeping those post-tax dollars where they are, the last thing you ever want to do is mix them with pre-tax dollars (from, say, your 401k).  As soon as you mix them, all the dollars become subject to pro-rata taxation (as Joe mentioned), so any future decision you were planning to make about what to do with just your post-tax dollars is moot -- you have given away your right to think separately about your pre- and post-tax dollars. As an example, let's say the accounts you want to combine look like this: In the future you decide you want to move $2,000 from the above account into a Roth.  Because you mixed the money, the IRS insists that your rollover consists of: So now you owe tax (and it's regular income tax, I believe, not even capital gains tax) on $1,500.  That was money that you socked away specifically to avoid taxes, and now you've gone and paid taxes on it!  Now, there are valid arguments for intentionally moving pre-tax dollars from a Traditional to a Roth like this, but the point is that you shouldn't even have to be having that argument -- you have post-tax dollars in your Traditional IRA that almost certainly belong in a Roth.  By mixing your 401k into your Traditional IRA, you can no longer do anything with just the post-tax dollars.  The IRS will forever insist that you do these pro-rated calculations. Say in the future you suddenly realize that a Roth is much better for your financial situation than a Traditional IRA.  (Or you might still prefer a Traditional IRA, but as explained in the next sentence it's not available to you.)  Unfortunately, because you're covered by a (new) 401k -- or maybe because you earn too much money to contribute pre-tax dollars to either a Traditional or Roth IRA -- you're out of luck.  You're simply not allowed to contribute to a Roth. Most people in this situation can make use of what's called a back-door Roth.  They contribute up to the maximum amount per year ($5,500 or whatever it is now) post-tax to a Traditional IRA and then immediately roll it over to their Roth.  You can still try this, but guess what?  Yep, because you're mixing these new post-tax dollars with pre-tax money in your Traditional IRA, every year your rollover will be tainted with that pre-tax money, diluting the whole point of the back-door Roth.  You'll be paying taxes on money you never wanted to pay taxes on, and you'll be leaving post-tax money behind in your traditional IRA. (If it sounds like I'm annoyed about this situation from personal experience, it's because I am. :) By doing the conversion first, you never mix pre- and post-tax money, and your money goes where you want it. Of course, assuming you eventually do roll over your 401(k) into a Traditional IRA, the Really Annoying Consequence above will still plague you, but at least you'll have cleanly converted that first post-tax amount. The plan is perfectly valid and legal as tax rules currently stand. There is no limit to the amount you can rollover or convert to Roth. Assuming your 401(k) is traditional pre-tax, you'll have to pay income taxes on the amount you convert above personal exemption + standard deduction, which is currently about $10k/year for single filers. The other caveat is you'll need funds to live off of while your conversion money is seasoning for 5 years in your Roth IRA. If you start the conversion while you are still working, you'll be paying taxes on it in your marginal bracket, which will negate much of the benefit of the pre-tax 401(k). If your living expenses are low, you can convert about $10k/year without federal income taxes, while living off capital gains from a taxable account which have a 0% rate in the 15%  income tax bracket (goes up to about $37k/year). "From your description, it seems that you should have $75k of ""basis"" (i.e. after-tax amount) in your Traditional IRA. (As others have mentioned in comments, you might have had to report this in the year it was rolled over. I will assume that you will have figured this out.) Having after-tax amounts in a Traditional IRA is tricky as you usually can't choose to take out only the after-tax portion. Withdrawals as well as conversions to Roth IRA must be ""pro-rata"", which means that the amount of pre-tax and post-tax money in the withdrawal or conversion follows the same proportion as in the IRA overall. So say 7.5% of your Traditional IRA is after-tax, and the other 92.5% is pre-tax, that means any withdrawal will consist of pre-tax and post-tax in those proportions. So e.g. if you withdraw or convert $1000, $75 will be post-tax and $925 will be pre-tax. So any withdrawal or conversion will consist overwhelmingly of pre-tax amounts, which will be taxed, and you may not want that at this time. There is one way to separate the pre-tax and post-tax amounts in a Traditional IRA, but it involves having an active 401(k) (which I doubt you have at this point as you're retired). Some 401(k) plans allow people to rollover funds from Traditional IRA into it. If they allow this, then you can use it to ""siphon"" only pre-tax money from the Traditional IRA, as IRS does not allow rollover of post-tax money into a 401(k). This way you can rollover the entire pre-tax amount of the Traditional IRA into the Traditional 401(k), leaving behind only after-tax money in the Traditional IRA, which you can immediately convert to Roth IRA with no tax." "Your real question, ""why is this not discussed more?"" is intriguing. I think the media are doing a better job bringing these things into the topics they like to ponder, just not enough, yet.  You actually produced the answer to How are long-term capital gains taxed if the gain pushes income into a new tax bracket? so you understand how it works.  I am a fan of bracket topping. e.g. A young couple should try to top off their 15% bracket by staying with Roth but then using pretax IRA/401(k) to not creep into 25% bracket.  For this discussion, 2013 numbers, a blank return (i.e. no schedule A, no other income) shows a couple with a gross $92,500 being at the 15%/25% line. It happens that $20K is exactly the sum of their standard deduction, and 2 exemptions.  The last clean Distribution of Income Data is from 2006, but since wages haven't exploded and inflation has been low, it's fair to say that from the $92,000 representing the top 20% of earners, it won't have many more than top 25% today. So, yes, this is a great opportunity for most people.  Any married couple with under that $92,500 figure can use this strategy to exploit your observation, and step up their basis each year. To littleadv objection - I imagine an older couple grossing $75K, by selling stock with $10K in LT gains just getting rid of the potential 15% bill at retirement. No trading cost if a mutual fund, just $20 or so if stocks.  The more important point, not yet mentioned - even in a low cost 401(k), a lifetime of savings results in all gains being turned in ordinary income. And the case is strong for 'deposit to the match but no no more' as this strategy would let 2/3 of us pay zero on those gains.  (To try to address the rest of your questions a bit - the strategy applies to a small sliver of people. 25% have income too high, the bottom 50% or so, have virtually no savings. Much of the 25% that remain have savings in tax sheltered accounts. With the 2013 401(k) limit of $17,500, a 40 year old couple can save $35,000. This easily suck in most of one's long term retirement savings. We can discuss demographics all day, but I think this addresses your question.) If you add any comments, I'll probably address them via edits, avoiding a long dialog below." "The translation scheme is detailed in IRS Publication 15, ""Employer's Tax Guide"". For the 2010 version, the information is in Section 16 on Page 37. There are two ways that employers can calculate the withheld tax amount: wage bracket and percentage. Alternatively, they can also use one of the methods defined in IRS Publication 15-A. I'll assume the person making $60k/yr with 10 allowances is paid monthly ($5000/period) and married. Using the wage bracket method, the amount withheld for federal taxes would be $83 per pay period. Using the percentage method, it would be $81.23 per pay period. I don't recommend that you use this information to determine how to fill out your W-4. The IRS provides a special online calculator for that purpose, which I have always found quite accurate. Note: ""allowances"" are not the same as ""dependents""; ""allowances"" are a more realistic estimation of your tax deductions, taking into consideration much more than just your dependents." Actually the Fidelity hypothetical example (with same marginal tax rates) is super misleading.  They are putting the money saved up front from the traditional 401k in to at taxable account. Why? If you put the actual money used for the Roth that would be saved into traditional 401k they look the same no matter the timeline (with a hypothetical unchanging tax rate). Check this out.  So there are only two things to consider when choosing traditional vs roth. "J - Approaching the answer from the W4 perspective (for calculation purposes) may be more trouble that it's worth. I'd strongly suggest you use tax software, whether it's the 2016 SW or a current year one, on line, to get an estimate of your total tax bill for the year. You can then look at your current run rate of tax paid in to see if you are on track. If you have a large shortfall, you can easily adjust your withholdings. If you are on track to get a large refund, make the adjustment so next year will track better. Note, a withholding allowance is equal to a personal exemption. Some think that ""4"" means 4 people in the house, but it actually means ""don't tax 4 x $4050"" as I have $16200 in combined people or tax deductions."