How to Use a 401(k) Calculator

Quick answer

What this calculator tells you

A 401(k) calculator estimates what your workplace retirement account could be worth when you retire. It combines your current balance, what you contribute each year, what your employer adds, and an assumed annual return. The Loan Lyze 401(k) calculator also applies the 2026 IRS limit for the age you enter, so a contribution rate that would exceed the limit is capped instead of overstated.

This guide shows how the projection is built, how an employer match works with real numbers, what the 2026 limits are, and which input mistakes distort the result most. Every example uses the calculator's default inputs, so you can open the tool and reproduce each figure.

Inputs that matter most

Start with documents rather than memory whenever possible. For this calculation, pay particular attention to:

• current balance and age
• contribution rate and employer match formula
• expected annual return, net of fees
• retirement age and pay growth

Use values that describe the same point in time. Mixing an old balance with a new rate or an annual cost with a monthly figure can make a polished result unreliable.

When this calculator is most useful

Use this tool early enough to improve the decision, but late enough that the inputs are grounded in real information. It is particularly useful when:

• ✓You want to see what your current contribution rate could grow to by your retirement age, using a return you choose rather than a generic one.
• ✓You want to check whether you are contributing enough to receive your employer's full match, and what a smaller or larger contribution would change.
• ✓You are weighing a raise, a higher contribution rate, or a later retirement age and want to see which one moves the result most.
• ✓You want to check that the contribution you have in mind fits under the 2026 limit for your age: $24,500, $32,500 from age 50, or $35,750 for ages 60 through 63.

It is less useful when the key facts are unknown, the options use different time periods, or the decision turns mainly on eligibility, contract language, taxes, or risks the calculator does not model. In those situations, gather the missing documents first and treat any early result as a rough range.

How the calculation works

The model turns the entered assumptions into a consistent comparison. It does not fill in facts that were not requested, predict changing markets, or reproduce an institution's underwriting system. That boundary matters: mathematical precision is not the same thing as certainty.

2026 401(k) contribution limits

For 2026 the IRS limit on employee elective deferrals is $24,500, up from $23,500 in 2025. Employees aged 50 and over can add a catch-up contribution, and employees aged 60 through 63 qualify for a higher one.

• Under 50: up to $24,500.
• Age 50 or over (outside 60–63): up to $32,500, which is $24,500 plus an $8,000 catch-up.
• Ages 60 through 63: up to $35,750, which is $24,500 plus an $11,250 catch-up.

These limits apply to what you contribute, not to what your employer adds. The calculator caps your first-year contribution at the limit for the age you enter. A separate overall limit applies to employee and employer contributions combined, and some plans set lower limits of their own; the calculator models neither. The figures come from the IRS announcement and Notice 2025-67 linked in the source note below.

How the employer match works, with numbers

A plan describes its match with two numbers: the share of your contribution the employer matches, and the cap on pay that share applies to. "50% of the first 6%" on a $100,000 salary means the employer adds up to $3,000, which is 50% of $6,000. The calculator takes both numbers as separate inputs. Here is what that plan pays at three contribution rates:

• Contribute 3% ($3,000): the employer adds $1,500, half the available match.
• Contribute 6% ($6,000): the employer adds $3,000, the full match.
• Contribute 10% ($10,000): the employer still adds $3,000, because the match stops at 6% of pay.

Because 3% captures only half the match, moving to 6% doubles both your contribution and the employer's. With the default inputs the projected balance at 65 rises from about $903,000 to about $1.42 million. Going from 6% to 10% adds about $464,000 more, with no additional match. Compared with the same 10% contribution and no employer match at all (about $1.54 million), the match is worth roughly $348,000 over 30 years in this scenario. Your plan's summary plan description has the exact formula and any vesting schedule.

Choosing a return assumption

The annual return is the input you control least and the one that moves the result most. With the default inputs, the projected balance at 65 is about $1.30 million at a 5% return, about $1.89 million at 7%, and about $2.79 million at 9%. A four-point swing in the assumption more than doubles the outcome.

None of these is a forecast. The calculator applies a constant return every year, while real returns vary and can be negative, and it does not deduct fund or plan fees. Use a return net of fees, and test the lower end of your range before relying on the higher one.

Worked example

See the method in context

Take a 35-year-old earning $100,000 with $50,000 already saved who plans to retire at 65. They contribute 10% of pay ($10,000), their employer matches 50% of contributions up to 6% of pay ($3,000), contributions grow 2% a year, and the account earns 7% a year. First-year contributions total $13,000.

Over 30 years the calculator projects about $1.89 million. Roughly $577,000 of that is money put in (the $50,000 starting balance plus 30 years of contributions, including the match) and about $1.31 million is modeled growth. This is a nominal, pre-fee, pre-tax figure. Treat it as one point on the range shown in the return section below, not as a promise.

After running the base case, change one important input at a time. A less favorable rate, cost, return, income, or holding period shows whether the conclusion is sturdy or depends on a narrow set of assumptions.

Build three scenarios, not one prediction

A single answer can create false confidence. Three deliberately different cases reveal both the likely range and the assumptions that deserve more investigation.

Keep all unchanged inputs identical across the three runs. That discipline makes the comparison explainable and prevents several moving assumptions from hiding what actually changed the answer.

How to read the result

Look beyond the largest number on the screen. Review the breakdown, the time horizon, and any balance or cost that remains at the end of the comparison. Ask whether the result still fits cash flow and whether it changes under a conservative scenario.

A projected return is an assumption, not a forecast, and fees, taxes, and inflation all reduce what the final balance can buy. The right next step is to compare the result with your latest plan statement and summary plan description, then re-run it with a lower return.

Common mistakes to avoid

• Entering the match as one number. A plan that matches 50% of the first 6% needs both figures; entering 6% as the match percentage would model a far larger match than the plan pays.
• Assuming you get the full match at any contribution rate. You only receive it by contributing up to the cap on pay. At 3% in the default scenario you collect $1,500 of a possible $3,000.
• Using a recent strong market run as the return. The result is very sensitive to this input, so test a lower figure and use a return net of fund expenses and plan fees.
• Reading the result as today's money. The projection is in future dollars and does not adjust for inflation, so a balance decades away buys less than the same number does now.
• Forgetting vesting. If your plan has a vesting schedule and you may leave before it completes, part of the employer match may not be yours.
• Treating the 2026 limit as fixed for the whole projection. The calculator caps only the first year; later limits will change, and a long projection near the limit may assume more than future limits allow.

Decision checklist

Before acting, work through these questions. A “no” does not automatically reject the option; it identifies where more evidence or a wider safety margin is needed.

1. 1Am I contributing at least enough to receive the full employer match my plan offers?
2. 2Did I enter the match as two numbers, the percentage the employer matches and the cap on pay it applies to, exactly as my plan document states them?
3. 3Does my planned contribution fit under the 2026 limit for my age, and does my plan impose a lower limit of its own?
4. 4Have I run the projection with a return lower than my base assumption, and would the plan still work?
5. 5Do I understand the result is in future dollars, before fees, taxes, and inflation, and treat it as a range instead of a target?

Key terms in plain English

Elective deferral

The part of your pay you choose to put into the 401(k). The IRS limits it each year: $24,500 for 2026 before any catch-up. Employer contributions do not count toward this limit.

Employer match

Money your employer adds based on what you contribute. Plans usually state it as a percentage of your contribution up to a cap on pay, such as 50% of the first 6%. You only receive the full match if you contribute up to the cap.

Catch-up contribution

An extra amount allowed once you are 50 or older: $8,000 in 2026, or $11,250 for ages 60 through 63. It raises the maximum you can defer to $32,500 or $35,750.

Vesting

The share of employer contributions you own. Many plans require several years of service before employer money is fully yours. The calculator treats all employer contributions as vested, so check your plan's schedule if you may leave early.

Frequently asked questions