Retirement Accounts Explained: 401(k), IRA, Roth IRA, SEP-IRA -- Contribution Limits, Rules, and Strategy

May 9, 2026 · guides · 15 min read

Retirement Accounts Explained: 401(k), IRA, Roth IRA, SEP-IRA -- Contribution Limits, Rules, and Strategy

Retirement accounts are among the most powerful wealth-building tools available to individual investors. The combination of tax advantages, compound growth, and decades of time can transform modest annual contributions into life-changing sums. But the landscape is complex -- multiple account types, contribution limits that change annually, income phase-outs, penalty rules, and strategic choices about which account to prioritize.

This guide covers every major retirement account type in depth: 401(k), Traditional IRA, Roth IRA, SEP-IRA, and Solo 401(k). It also addresses advanced strategies including the backdoor Roth, mega backdoor Roth, Roth conversion ladders for early retirement, and 72(t) SEPP withdrawals. All contribution limits reflect 2024 figures.

The 401(k): Employer-Sponsored Plans

The 401(k) is the most common employer-sponsored retirement plan in the United States. It allows employees to defer a portion of their salary into a tax-advantaged account, reducing taxable income in the year of contribution (for traditional 401(k)) or contributing after-tax dollars for tax-free growth (for Roth 401(k)).

2024 Contribution Limits

For 2024, the employee contribution limit to a 401(k) is $23,000. Employees who are age 50 or older by the end of the calendar year can make an additional catch-up contribution of $7,500, bringing the total potential employee deferral to $30,500.

These limits apply to the combined total of employee contributions across all 401(k) plans at all employers. If someone holds two jobs and participates in both employers' 401(k) plans, the $23,000 ceiling applies in aggregate, not per plan.

The total annual additions limit -- which includes both employee and employer contributions -- is $69,000 in 2024 (or $76,500 with catch-up). This matters primarily for high-income earners and self-employed individuals using advanced strategies.

Traditional vs. Roth 401(k)

Many employers now offer both traditional and Roth options within the same 401(k) plan. The mechanics differ in one critical way: timing of the tax break.

With a traditional 401(k), contributions reduce your taxable income today. If you earn $120,000 and contribute $23,000, your W-2 income for federal tax purposes drops to $97,000. The money grows tax-deferred, and withdrawals in retirement are taxed as ordinary income.

With a Roth 401(k), contributions are made with after-tax dollars -- no reduction in current taxable income. The money grows tax-free, and qualified withdrawals in retirement are completely tax-free, including earnings. Unlike the Roth IRA, the Roth 401(k) has no income limit for eligibility.

The traditional vs. Roth decision comes down to whether your marginal tax rate today is higher or lower than you expect it to be in retirement. Younger workers in lower tax brackets generally benefit more from Roth contributions. Higher earners near peak income years often extract more value from traditional contributions and the immediate tax deduction.

Employer Match: Guaranteed Return on Contribution

The employer match is one of the few genuine guaranteed returns available in investing. If your employer matches 100% of contributions up to 3% of salary, contributing that 3% immediately doubles your effective return before the market does anything.

A $90,000 earner contributing 3% ($2,700) receives a $2,700 employer match -- a 100% return before any investment gain. No asset class consistently delivers that. Capturing the full employer match should be the first allocation priority for any investor with access to a 401(k) match, before taxable investing, before other accounts, before paying down moderate-interest debt.

Vesting Schedules

Employer match contributions are subject to vesting schedules. Your own contributions are always 100% vested immediately -- they belong to you regardless of when you leave. But employer contributions may vest gradually or only after a minimum tenure.

Common structures include cliff vesting (0% until a defined tenure, then 100% -- for example, 0% vested for two years, then fully vested) and graded vesting (a percentage per year -- for example, 20% per year over five years). Before leaving a job, it is worth calculating unvested employer contributions, which can represent thousands of dollars forfeited.

Investment Menu Limitations

A structural drawback of 401(k) plans is that investment options are selected by the plan sponsor, not the participant. Many corporate plans offer a limited menu -- sometimes 15 to 25 options -- that may include high-expense-ratio funds or no access to asset classes like international small-cap or individual securities.

The standard best practice within a 401(k) is to identify the lowest-cost broad-market index funds available -- typically an S&P 500 index fund, a total market fund, and a bond index fund -- and use those as the core building blocks. Avoid target-date funds with expense ratios above 0.15%, which is attainable at most plans that include Vanguard, Fidelity, or Schwab institutional funds.

Traditional IRA: Individual Retirement Account

The Traditional IRA is an individually owned retirement account, not tied to employment. Anyone with earned income (wages, self-employment income) can contribute, up to the annual limit.

2024 Contribution Limits

The 2024 IRA contribution limit is $7,000. Investors age 50 or older can make an additional $1,000 catch-up contribution for a total of $8,000. This limit applies across both Traditional and Roth IRAs combined -- it is not $7,000 per account type, but $7,000 in total across all your IRAs.

Deductibility Rules for Covered Employees

Whether your Traditional IRA contribution is tax-deductible depends on whether you (or your spouse) are covered by a workplace retirement plan and your modified adjusted gross income (MAGI).

If neither you nor your spouse is covered by a workplace plan, contributions are fully deductible regardless of income.

If you are covered by a workplace plan in 2024, the deduction phases out at:

If your spouse is covered by a workplace plan but you are not, your deduction phases out at:

A non-deductible Traditional IRA contribution still provides tax-deferred growth. However, in this case the Roth IRA or backdoor Roth strategy (covered below) is usually superior.

Required Minimum Distributions

Traditional IRA funds cannot grow tax-deferred forever. The IRS requires account holders to begin taking Required Minimum Distributions (RMDs) starting at age 73, as established by the SECURE 2.0 Act. The RMD amount is calculated by dividing the prior year-end account balance by an IRS life expectancy factor from Uniform Lifetime Tables.

Failing to take the full RMD results in a 25% excise tax on the amount that should have been withdrawn (reduced to 10% if corrected promptly). RMDs are taxed as ordinary income and can push retirees into higher tax brackets or trigger Medicare IRMAA surcharges on premiums.

This is one of the key arguments for Roth conversions during the pre-RMD years: systematically moving money from Traditional to Roth accounts at a controlled tax rate to reduce the future RMD burden.

Early Withdrawal Penalty and Exceptions

Withdrawals from a Traditional IRA before age 59.5 are subject to a 10% early withdrawal penalty in addition to ordinary income tax. However, the tax code provides numerous exceptions:

These exceptions waive the penalty but not the ordinary income tax.

Roth IRA: Tax-Free Growth

The Roth IRA is the mirror image of the Traditional IRA in tax treatment: contributions are made after tax (no deduction), but qualified withdrawals -- including all earnings -- are completely tax-free.

2024 Limits and Income Phase-Outs

The Roth IRA contribution limit matches the Traditional IRA: $7,000 per year ($8,000 for age 50+), with the combined IRA limit applying across both accounts.

Unlike the Traditional IRA, the Roth IRA has income eligibility limits for direct contributions. In 2024:

These limits apply only to direct contributions. The backdoor Roth strategy (below) provides an alternative path for high earners.

Tax-Free Growth and Qualified Withdrawals

Qualified Roth IRA withdrawals are defined as those made after the account has been open for at least five years AND the account holder is age 59.5 or older, disabled, deceased, or using up to $10,000 for a first home purchase. Meeting both conditions means all withdrawals -- contributions and earnings -- are fully tax-free.

This makes the Roth IRA particularly valuable for younger investors and anyone expecting higher tax rates in retirement than in their current accumulation years.

No RMDs During Owner's Lifetime

A critical advantage of the Roth IRA: the owner is never required to take distributions during their lifetime. This makes the Roth IRA the ideal account for leaving tax-free money to heirs, who will be subject to the 10-year rule under the SECURE Act for inherited accounts. It also allows retirees to leave Roth funds untouched, compounding indefinitely, while drawing from taxable and Traditional IRA accounts first.

Contribution (Not Earnings) Withdrawal Flexibility

A frequently misunderstood feature: Roth IRA contributions (not earnings) can be withdrawn at any time, at any age, without taxes or penalties. Because you already paid tax on the money before contributing, the IRS imposes no restriction on withdrawing the original contribution amount.

This makes the Roth IRA function as an emergency fund of last resort for disciplined investors. If you have contributed $40,000 to a Roth IRA over several years and the account has grown to $60,000, you can withdraw up to $40,000 at any time without consequence. Only the $20,000 in earnings is subject to the five-year and age-59.5 rules.

Backdoor Roth IRA: The High-Earner Workaround

For investors whose income exceeds the Roth IRA direct contribution limits, the backdoor Roth provides an alternative path.

The Basic Strategy

The mechanics:

  1. Make a non-deductible contribution to a Traditional IRA (up to $7,000 in 2024). Because you are over the income limit for deductibility, this contribution has no tax deduction but still goes into the account.
  2. Convert the Traditional IRA to a Roth IRA. If done shortly after contribution, there is minimal or no earnings to tax at conversion.
  3. The result is the functional equivalent of a direct Roth IRA contribution -- money in a Roth account that will grow tax-free.

This strategy has been in use for many years and is widely accepted by the IRS, despite periodic legislative threats to close it.

The Pro-Rata Rule Problem

The backdoor Roth strategy works cleanly only if you have no pre-tax Traditional IRA money. If you have existing Traditional IRA balances (including rollover IRAs from old 401(k) plans), the IRS applies the pro-rata rule when calculating the taxable portion of a conversion.

Example: You have $50,000 in a rollover IRA (pre-tax) and contribute $7,000 non-deductibly to a Traditional IRA for the backdoor conversion. Your total IRA balance is $57,000. The non-deductible portion is $7,000 / $57,000 = 12.3%. Only 12.3% of your Roth conversion is tax-free. The remaining 87.7% is taxed as ordinary income.

The standard solution for high earners with existing Traditional IRA balances is to roll those IRAs into a current employer's 401(k) plan (if the plan accepts rollovers), clearing the pre-tax IRA balance and enabling a clean backdoor Roth.

Mega Backdoor Roth: After-Tax 401(k) Contributions

The mega backdoor Roth is an advanced strategy for high earners who have maximized all standard contribution limits and want to move more money into Roth treatment. It is significantly less accessible than the backdoor Roth -- only a subset of 401(k) plans support the required plan features.

How It Works

The total 401(k) annual additions limit in 2024 is $69,000 (employee + employer). An employee who contributes $23,000 in elective deferrals and receives, say, $10,000 in employer match has $36,000 of remaining space under the total limit.

Some plans allow employees to fill that remaining space with after-tax (non-Roth) contributions -- money contributed after income taxes, beyond the $23,000 employee deferral limit. These after-tax contributions grow tax-deferred but would be taxed on withdrawal if left in place.

The strategy: once after-tax contributions are made, they are converted to Roth either through an in-plan conversion (if the plan allows in-plan Roth conversions) or through an in-service distribution to a Roth IRA (if the plan allows distributions while still employed). The result is Roth money, contributed at the effective $69,000 total limit rather than the $23,000 deferral limit.

Plan Support Requirement

This strategy requires that your employer's 401(k) plan explicitly allow after-tax contributions AND allow either in-plan Roth conversions or in-service distributions. Many plans do not support these features. Check your plan's Summary Plan Description (SPD) or ask your HR or benefits administrator directly. Companies known to offer mega backdoor Roth capability include several large technology and finance employers, but plan documents vary.

SEP-IRA: For Self-Employed and Small Business Owners

The Simplified Employee Pension IRA is designed for self-employed individuals and small business owners who want a straightforward, high-contribution retirement account.

2024 Contribution Limits

Contributions to a SEP-IRA can be up to 25% of net self-employment compensation, with a maximum of $69,000 for 2024. For a self-employed individual, net compensation is calculated after the deduction for self-employment tax.

Example: A sole proprietor with $200,000 in net self-employment income (after SE tax deduction) can contribute $50,000 to a SEP-IRA in 2024 -- far more than the $7,000 IRA limit or even the $23,000 employee deferral limit.

Importantly, there are no catch-up contributions for the SEP-IRA. This differentiates it from the Solo 401(k), which supports catch-up deferrals.

Simplicity vs. Flexibility

The SEP-IRA is administratively simple -- no Form 5500 filing, no annual testing, no complex plan documents. Contributions can be made up to the tax filing deadline (including extensions), making it useful for year-end tax planning.

The trade-off is flexibility. If a SEP-IRA plan covers a business with employees, the same percentage contribution must be made for all eligible employees, which can create significant costs. For businesses with employees, a Solo 401(k) or SIMPLE IRA may be more practical.

Solo 401(k): Maximum Flexibility for Self-Employed

The Solo 401(k) -- also called the Individual 401(k) or One-Participant 401(k) -- is available to self-employed individuals and business owners with no full-time employees other than themselves and a spouse.

2024 Contribution Structure

The Solo 401(k) allows contributions in two roles:

As employee: up to $23,000 in elective deferrals ($30,500 if age 50+). This is the same as a regular 401(k).

As employer: up to 25% of net self-employment compensation as a profit-sharing contribution.

Combined, both components can reach the $69,000 total limit ($76,500 with catch-up). This makes the Solo 401(k) superior to the SEP-IRA for self-employed individuals with moderate income -- because the employee deferral component allows hitting higher contribution amounts at lower income levels.

Example comparison at $100,000 net self-employment income:

The Solo 401(k) can also include a Roth deferral option (same $23,000 limit), which is not available with the SEP-IRA.

The administrative cost is modest but higher than a SEP-IRA -- plans must file Form 5500-EZ once assets exceed $250,000, and plan documents are required. Most major brokerages (Fidelity, Vanguard, Charles Schwab) offer no-cost Solo 401(k) plans.

Asset Location Strategy: Which Investments Belong Where

Having multiple account types creates an optimization opportunity: placing each asset class in the account where it is taxed most efficiently. This is called asset location, and it can add meaningful after-tax returns without changing your overall portfolio allocation.

The Core Principle

Different assets generate different types of taxable events:

The goal is to hold ordinary-income-generating assets in tax-advantaged accounts, while holding assets taxed at favorable rates in taxable accounts.

Practical Placement Guidelines

Tax-deferred accounts (Traditional IRA, 401(k)) are best suited for:

Roth IRA is best suited for:

Taxable accounts are best suited for:

This framework does not change your overall asset allocation -- the combined portfolio across all accounts remains your target. It only changes which account holds which piece of that allocation.

Roth Conversion Ladder for Early Retirement

For investors pursuing Financial Independence / Early Retirement (FIRE) -- planning to retire well before age 59.5 -- accessing retirement funds without penalty requires advance planning. The Roth conversion ladder is the primary vehicle.

The Problem

Standard retirement accounts impose a 10% penalty on withdrawals before age 59.5. An investor who retires at 45 with substantial 401(k) and IRA balances faces a 14.5-year gap before penalty-free access. They need a bridge.

The Five-Year Conversion Strategy

Each Roth conversion becomes available penalty-free after a five-year holding period from the date of conversion. (This is separate from the five-year rule for Roth contributions.) The strategy:

  1. Begin converting Traditional IRA funds to Roth IRA each year, starting at least five years before the money is needed.
  2. Convert only as much as fills up low tax brackets (often the 12% or 22% bracket in a year of no earned income).
  3. After five years, each year's conversion is available for penalty-free withdrawal.

Example: An investor retires at 45 with $800,000 in a Traditional IRA and minimal taxable income. They convert $40,000 per year to Roth. By age 50, the first $40,000 conversion (made at 45) is accessible penalty-free. By age 51, the conversion from age 46 is accessible, and so on.

The ladder requires:

This is one of the most powerful strategies for early retirees, allowing full utilization of tax-deferred retirement balances without penalty.

72(t) SEPP: Penalty-Free Early IRA Access

Substantially Equal Periodic Payments (SEPP) under IRC Section 72(t) provide another mechanism for penalty-free withdrawals from an IRA before age 59.5. It is more rigid than the Roth conversion ladder but does not require a five-year advance runway.

How It Works

Once established, a 72(t) program requires the account holder to take distributions from the IRA at least annually, for the longer of five years or until they reach age 59.5. The payments must be substantially equal -- calculated using one of three IRS-approved methods -- and the schedule cannot be modified once started without triggering the 10% penalty on all previous distributions retroactively.

The Three Calculation Methods

The Required Minimum Distribution method divides the account balance by the IRS life expectancy factor each year. This produces the smallest and most variable payments, since the calculation is redone annually.

The Amortization method calculates a fixed annual payment based on the account balance, a reasonable interest rate (capped at 120% of the federal mid-term rate), and a life expectancy factor. This typically produces larger, fixed payments than the RMD method.

The Annuitization method calculates payments by dividing the account balance by an annuity factor derived from the applicable mortality table and interest rate. It also produces fixed payments and typically amounts similar to the amortization method.

The amortization and annuitization methods lock in a fixed payment that provides predictability. For an investor retiring early with a specific income target, these methods allow planning around a known annual distribution.

Consequences of Modification

If the 72(t) schedule is modified before both the five-year term and age 59.5 are satisfied, the 10% penalty is recaptured on all prior distributions that benefited from the exception, plus interest. This is a severe consequence that makes 72(t) programs appropriate only when the investor is confident the fixed payment structure will work for the entire period.

One exception: a one-time change from the amortization or annuitization method to the RMD method is permitted without triggering recapture.

Putting It Together: Retirement Account Contribution Hierarchy

Given the range of account options, a general prioritization framework:

  1. Contribute to 401(k) up to the full employer match (capture guaranteed return first)
  2. Maximize HSA if enrolled in a qualifying high-deductible health plan (triple tax advantage)
  3. Maximize Roth IRA ($7,000) if income eligible, or backdoor Roth if above the limit
  4. Return to 401(k) and maximize employee deferral to $23,000
  5. If self-employed, maximize SEP-IRA or Solo 401(k) instead of steps 1 and 4
  6. If high earner with supporting 401(k) plan features, explore mega backdoor Roth to $69,000
  7. Any remaining investable funds go to taxable brokerage accounts

The specific order may shift based on current vs. expected future tax rates, access to employer match, and whether the investor is self-employed. But this hierarchy captures the general after-tax value ranking of each account type.

Key Numbers Summary (2024)

401(k) employee deferral: $23,000 ($30,500 with catch-up at 50+) Total 401(k) plan limit (employee + employer): $69,000 ($76,500 with catch-up) Traditional IRA and Roth IRA combined: $7,000 ($8,000 with catch-up at 50+) Roth IRA income phase-out (single): $146,000 - $161,000 Roth IRA income phase-out (married filing jointly): $230,000 - $240,000 Traditional IRA deductibility phase-out (single, covered by workplace plan): $77,000 - $87,000 SEP-IRA maximum: $69,000 (25% of compensation) Solo 401(k) maximum: $69,000 combined ($76,500 with catch-up) RMD start age: 73

Understanding these account types, limits, and rules is foundational to building a tax-efficient retirement portfolio. The specific choices -- Traditional vs. Roth, when to convert, how to sequence withdrawals -- depend on individual tax situations, income trajectory, and retirement timeline. This framework provides the structure; the inputs vary by investor.

All figures reflect 2024 IRS limits. Contribution limits are adjusted for inflation periodically. Verify current-year limits at IRS.gov before contributing.