Overview
The 401(k) is the most powerful retirement savings vehicle available to most American workers. It combines tax advantages, an employer match, and contribution limits nearly three times an IRA's, which is why it's the first account worth funding in any retirement strategy.
This guide covers every decision along the way: how much to contribute, how to capture the full match, whether to choose traditional or Roth, and how to pick investments that compound without piling on unnecessary cost.
What you need before you start:
- Your current annual salary
- Your employer's match formula (check your Summary Plan Description or HR portal)
- Your current 401(k) balance
- Your estimated years to retirement
The 401(k) Calculator models how different contribution rates translate into a retirement corpus, and the 401(k) Contribution Calculator finds the exact payroll percentage to elect.
Step 1: Know the 2026 Contribution Limits
The IRS sets annual limits on 401(k) contributions. For 2026:
| Contribution Type | Annual Limit |
|---|---|
| Employee elective deferral (under 50) | $23,500 |
| Catch-up contribution (age 50–59) | +$7,500 → $31,000 |
| Super catch-up (age 60–63) | +$3,750 → $34,750 |
| Combined employee + employer (under 50) | $70,000 |
The catch-up provision accelerates things quite a bit. A 55-year-old maxing out contributions at $31,000 a year for 10 years at a 7% average return accumulates roughly $428,000 in that decade alone, before factoring in any existing balance.
If you're between 60 and 63, the super catch-up (introduced under SECURE 2.0) is worth paying attention to: the extra $3,750 on top of the standard catch-up applies only to this age window and doesn't extend to age 64.
Step 2: Always Capture the Full Employer Match First
The employer match is the best guaranteed return you'll find on any investment, typically 50% on the spot, before market returns even enter the picture.
Example, $100,000 salary, 50% match on up to 6%:
| Your Contribution | Employer Match | Total Invested |
|---|---|---|
| 3% ($3,000) | $1,500 | $4,500 |
| 6% ($6,000) | $3,000 | $9,000 |
| 10% ($10,000) | $3,000 | $13,000 |
Contribute below 6% in this example and you're leaving employer money on the table. Contributing above 6% is still smart, just know those extra dollars don't get matched.
Common match formulas to look for on your Summary Plan Description:
- 50% of the first 6% of salary (most common)
- 100% of the first 3% of salary
- 25% of the first 8% of salary
Hit the full match threshold before sending dollars anywhere else. It's the single highest-leverage move available to most employees.
Step 3: Choose Traditional or Roth 401(k)
Many employers now offer both. The decision comes down to one question: will your marginal tax rate be higher now or in retirement?
Traditional 401(k):
- Contributions are pre-tax, so your taxable income drops today
- Money grows tax-deferred
- Withdrawals in retirement get taxed as ordinary income
- Works best when your current tax rate beats your expected retirement rate
Roth 401(k):
- Contributions are after-tax, no upfront deduction
- Money grows tax-free
- Qualified withdrawals in retirement come out completely tax-free
- Works best when your current tax rate sits below your expected retirement rate
As a rough guide, early-career workers in the 22% bracket or below usually benefit from Roth. Workers in the 32% bracket or above usually benefit from traditional. Workers in the 24% bracket sit in judgment-call territory, and splitting contributions between both hedges against whatever tax changes come later.
The Roth vs Traditional IRA Calculator models your specific numbers against your current and projected future income.
Step 4: Calculate Your Projected Corpus
Compounding rewards time more than any other variable in this whole process. Run these scenarios through the 401(k) Calculator to see what your contribution rate actually produces:
Scenario: $1,200/month contribution ($14,400/year), 8% average annual return
| Starting Age | Years Invested | Ending Corpus at 65 |
|---|---|---|
| 25 | 40 years | ~$3.5 million |
| 30 | 35 years | ~$2.5 million |
| 35 | 30 years | ~$1.6 million |
| 40 | 25 years | ~$1.1 million |
Waiting 10 years, from age 25 to 35, costs roughly $1.9 million at retirement. No investment strategy makes up that gap as efficiently as just starting earlier.
The 8% figure represents an approximate long-run US equity market average in nominal terms. Use 5 to 6% for more conservative modelling, or for years close to retirement.
Step 5: Set Your Contribution Percentage via Payroll
Your 401(k) election gets set as a percentage of gross salary through payroll or your HR portal. The 401(k) Contribution Calculator finds the exact percentage to elect.
Target contribution rates by situation:
| Situation | Recommended Contribution |
|---|---|
| Minimum, capture full match only | Whatever hits the match threshold |
| Standard retirement saver | 15% of gross salary (including employer match) |
| Aggressive saver / late starter | 20–25% of gross salary |
| Maxing out under 50 | $23,500 ÷ annual salary |
| Maxing out age 50+ | $31,000 (or $34,750 if 60–63) ÷ annual salary |
If 15% feels out of reach right now, start at the match threshold and add 1% with each pay raise. Most employees barely notice the difference in take-home pay, since the raise partially offsets the increase and the pre-tax contribution lowers taxable income at the same time.
Step 6: Choose Your Investment Allocation
Your contribution rate sets how much goes in. Your investment allocation sets how it grows.
Option A, Target-Date Funds (recommended for most investors)
Pick the fund with the year nearest your planned retirement, a 2055 Target Date Fund for a 30-year-old planning to retire around 2055, say. The fund shifts automatically from aggressive equity exposure toward a more conservative bond-heavy mix as you approach the target date. Index-based target-date funds typically run 0.10 to 0.15% per year in costs.
Option B, DIY Index Fund Portfolio
A simple rule: subtract your age from 110 to get your equity percentage.
- Age 30: 80% equities, 20% bonds
- Age 40: 70% equities, 30% bonds
- Age 50: 60% equities, 40% bonds
Within equities, spread across US large-cap, US small-cap, and international index funds, and rebalance once a year back to your target. Keep expense ratios down. Every 0.50% in extra annual fees costs roughly $100,000 on a $500,000 portfolio over 20 years.
Expense ratio benchmark:
- Excellent: below 0.10%
- Acceptable: 0.10–0.30%
- High: above 0.50%, switch if an index alternative exists in your plan
After-Tax 401(k) Contributions and the Mega Backdoor Roth
High earners who've already hit the $23,500 employee limit and want to save more can look into after-tax contributions. The combined employee-plus-employer limit for 2026 is $70,000. If your plan allows after-tax contributions beyond the $23,500 elective deferral, you can contribute the difference, roughly $40,000 to $46,500 depending on your employer match.
If your plan also allows in-plan Roth conversions or in-service withdrawals, you can convert those after-tax dollars to Roth. That's the mega backdoor Roth strategy, and it delivers tax-free growth on a much larger sum than the standard $23,500 limit allows on its own.
Check your Summary Plan Description for two specific features: "after-tax employee contributions" and "in-service withdrawals" or "in-plan Roth conversions." Find both, and the mega backdoor Roth is available to you.
Vesting Schedule, Know When the Match Is Truly Yours
Your own contributions are always 100% yours, immediately. Employer contributions follow a vesting schedule instead.
Immediate vesting means the employer match is yours from day one. Cliff vesting means you own 0% until a specific anniversary, often 3 years, then jump to 100%. Graded vesting phases ownership in over 2 to 6 years, say 20% per year.
If you're weighing whether to leave a job, check your vesting date first. Leaving two months before a cliff vesting date could forfeit thousands of dollars in employer contributions. Many HR portals show your vesting percentage right in the 401(k) summary dashboard.
What Happens When You Change Jobs
Leave an employer and you've got four options for your 401(k) balance.
Rolling into your new employer's 401(k) is simplest if the new plan has decent investment options and low costs. Rolling into a traditional IRA gives you the widest investment selection with no immediate tax consequence. Leaving it with your old employer is fine if the balance tops $5,000 and you like the existing plan's options. Cashing out triggers income tax plus a 10% early withdrawal penalty if you're under 59½, and it's almost never the right move.
A direct rollover moves funds from the old 401(k) to the new account without ever touching your hands, so no taxes get withheld. An indirect rollover has the old plan withhold 20% for taxes, and you have to deposit the full pre-withholding amount into the new account within 60 days to avoid tax on that withheld portion.
Required Minimum Distributions from traditional 401(k) accounts start at age 73 under current law. Rolling an old 401(k) into a Roth IRA eliminates RMDs entirely on that balance.
Key Terms
- 401(k): an employer-sponsored defined-contribution retirement plan with pre-tax or Roth contribution options
- Vesting: the schedule by which employer contributions become permanently owned by the employee
- Roth: a designation for after-tax contributions that grow and get withdrawn tax-free in retirement
- Required Minimum Distribution (RMD): the minimum annual withdrawal the IRS requires from traditional retirement accounts starting at age 73