Oblivious Investor

A reader writes in, asking:

“I am tentatively starting to think how taxes affect retirement especially for the ACA purposes, in case it somehow survives the latest current court fight. So, which kind of tax should we be concerned about? When I google this, I can find someone saying ‘marginal tax’ whereas somebody else saying ‘effective tax rate’. So, which is it? Could you direct me to some easy to understand tutorial about it? I certainly cannot plan anything (e.g. 401k to an IRA and then Roth IRA conversions) and staying under ‘the cliff’ unless I understand the basics on this subject.”

Broadly speaking:

• Effective tax rate is useful for budgeting;
• Marginal tax rate is useful for tax planning.

For example, if you’re considering taking a new job and you want to know how much actual take-home pay you would have, given a certain level of gross salary, you’d need to know your effective tax rate. (“How much total tax would I be paying on my total income?”)

But for almost every tax planning decision, we want to know marginal tax rate. For instance, if you were considering a Roth conversion, you’d need to know the applicable marginal tax rate. (“How much tax would I pay on this income?”)

With tax planning, we’re generally trying to decide “should I do X or should I do Y?” And we want to know how the tax bill changes as a result of doing X instead of doing Y. That is, we want to know the marginal tax rate.

This is the case whenever we’re trying to determine the value of a potential deduction (e.g., additional deductible charitable contributions). And it’s the case whenever we’re trying to determine the tax-cost of potential additional income (e.g., additional distributions from tax-deferred accounts). It’s also the case when trying to determine when it’s best to recognize a certain piece of income (e.g., doing a Roth conversion this year as opposed to in a later year).

In all of those cases, marginal tax rate is what we want to know.

What’s Your Marginal Tax Rate?

An important point about marginal tax rates is that there’s more to it than just looking at what tax bracket you’re in. Your actual marginal tax rate for a given type of income could be significantly higher or lower than your tax bracket. This is often the case when additional income causes you to lose out on a particular tax break for which you currently qualify (e.g., your income becomes too high to qualify for a given credit, or a greater percentage of your Social Security benefits become taxable). And the opposite can happen with deductions. That is, in some cases a deduction will cause not only the anticipated amount of savings (i.e., the amount of the deduction times your tax bracket) but also additional savings because now your income is low enough to qualify for some other tax break.

In addition, certain types of income (most importantly, qualified dividends and long-term capital gains) are taxed at different tax rates than ordinary income. Also, when doing the eligibility calculation for various tax breaks, some types of income/deductions count, while others do not — and it varies depending on which deduction/credit we’re talking about.

In my opinion, the best tool for people doing their own tax planning is tax preparation software. You can create a hypothetical return, look at the total tax due, then adjust one factor (e.g., “what if I took another $1,000 from my traditional IRA this year?”). When you see how much your total tax would change, you know your actual marginal tax rate for that hypothetical income/deduction.

The IRS recently published the annual inflation updates for 2021. If you have questions about a particular amount that I do not mention here, you can likely find it in the official IRS announcements:

• Rev. Proc. 2020-45 contains most inflation adjustment figures, and
• Notice 2020-79 contains figures relating to retirement accounts.

Single 2021 Tax Brackets

Married Filing Jointly 2021 Tax Brackets

Head of Household 2021 Tax Brackets

Married Filing Separately 2021 Tax Brackets

Standard Deduction Amounts

The 2021 standard deduction amounts are as follows:

• Single or married filing separately: $12,550
• Married filing jointly: $25,100
• Head of household: $18,800

The additional standard deduction for people who have reached age 65 (or who are blind) is $1,350 for each married taxpayer or $1,700 for unmarried taxpayers.

IRA Contribution Limits

The contribution limit for Roth IRA and traditional IRA accounts is unchanged at $6,000.

The catch-up contribution limit for people age 50 or over does not get inflation adjustments and therefore is still $1,000.

401(k), 403(b), 457(b) Contribution Limits

The salary deferral limit for 401(k) and other similar plans is unchanged at $19,500.

The catch-up contribution limit for 401(k) and other similar plans for people age 50 and over is unchanged at $6,500.

The maximum possible contribution for defined contribution plans (e.g., for a self-employed person with a sufficiently high income contributing to a solo 401(k)) is increased to $58,000.

Child Tax Credit

The child tax credit ($2,000 per child) and the related phaseout threshold ($200,000 of modified adjusted gross income, $400,000 if married filing jointly) do not get inflation adjustments. The portion of the credit that can be refundable (up to $1,400 per child) does receive inflation adjustments, but it is still $1,400 for 2021.

Capital Gains and Qualified Dividends

For 2021, long-term capital gains and qualified dividends face the following tax rates:

• 0% tax rate if they fall below $80,800 of taxable income if married filing jointly, $54,100 if head of household, or $40,400 if filing as single or married filing separately.
• 15% tax rate if they fall above the 0% threshold but below $501,600 if married filing jointly, $473,750 if head of household, $445,850 if single, or $250,800 if married filing separately.
• 20% tax rate if they fall above the 15% threshold.

Alternative Minimum Tax (AMT)

The AMT exemption amount is increased to:

• $73,600 for single people and people filing as head of household,
• $114,600 for married people filing jointly, and
• $57,300 for married people filing separately.

Estate Tax

The estate tax exclusion is increased to $11,700,000 per decedent.

Pass-Through Business Income

With respect to the 20% deduction for qualified pass-through income, for 2021, the threshold amount at which the “specified service trade or business” phaseout and the wage (or wage+property) limitations begin to kick in will be $329,800 for married taxpayers filing jointly, $164,900 for single taxpayers and people filing as head of household, or $164,925 for married people filing separately.