Get the match. Then let time work.

A typical U.S. 401(k) match might be 50% of your deferral up to 6% of salary — or 100% on the first 3% plus 50% on the next 2%. Leaving an unvested or uncaptured match on the table is a pay cut. Vesting schedules exist: you may need years of service before the match is fully yours. Even then, the contribution still belongs in the first conversation, before you debate Roth vs traditional on a spreadsheet.

Read the summary plan description. “We match 50%” without a cap is rare. “We match 50% of 6%” means a 3% of salary match if you defer 6%. Contribute less than 6% and you leave part of the match. Contribute more and you are saving extra — good — but the free slice stopped at the cap.

Compounding is slow, then less slow

Compounding is not a magic trick. It is return earned on prior return. A chart that starts at $25,000 and adds $500 a month looks boring for ten years and dramatic at year 30 if the average return is in the high single digits. The boring decade is why people quit. The dramatic decade is why they wish they had not.

A constant 7% slider is a teaching tool. Real years include −20% and +25%. Sequence matters more when you are withdrawing (see the FIRE guide) than when you are adding every paycheck. While working, the usual failure mode is not picking the wrong fund; it is pausing contributions after a crash or cashing out at a job change. Rollover the old 401(k). Do not treat a $8,000 balance as “fun money.”

Traditional 401(k) vs Roth

A traditional 401(k) often lowers taxable wages now. A Roth 401(k) or Roth IRA uses after-tax dollars; qualified withdrawals in retirement can be tax-free. Contribution limits, income phaseouts for IRAs, and required minimum distributions change by year. The growth curve can look similar; the tax bill does not.

This site’s growth calculator shows account balance, not after-tax spending money. A traditional balance is pre-tax. You will owe tax later at unknown rates. A Roth balance is closer to spendable if rules are met. Comparing them as if $500,000 were the same kind of dollar is a common mistake.

High earners sometimes hit IRA income limits for direct Roth contributions and use other paths. That is beyond a compound-interest toy. Capture the 401(k) match first either way; match dollars are usually traditional even if your deferral is Roth, depending on the plan. Check the plan. Do not assume.

Match vs mortgage vs emergency fund

Personal-finance order-of-operations arguments never end. A durable version for most W-2 households: keep a small cash buffer so you do not raid the 401(k), contribute enough to get the full match, high-interest debt next, then extra retirement or extra mortgage principal depending on rate and job stability. A 24% card beats a 7% expected market return. A 3% mortgage does not automatically beat investing, and it does not automatically lose. The calculator will not choose for you; it will show how match and time change a balance.

Job changes and leftover plans

When you leave an employer, the 401(k) does not vanish. You can generally leave it (if the plan allows), roll it to an IRA, or roll it to a new employer’s plan. Cashing out is usually the expensive option: income tax, a possible 10% additional tax if you are under 59½, and a hole in compounding that a later “I’ll catch up” rarely fills. A $8,000 cash-out at 32 is not $8,000 of fun; it is the seed of a much larger number at 62 that you will not have.

Company stock inside a plan has extra tax rules (net unrealized appreciation) that this site does not model. If a large slice of your net worth is one ticker, that is a concentration problem first and a calculator problem second.

A worked example

Salary $78,000, 6% employee deferral, 50% match on 6%, 7% assumed return, 30 years, starting at $10,000. Set match to zero, note year-30 balance, then restore the match. The gap is the cost of “I’ll increase later.” Then cut the return to 5%. The gap is still large because match is extra principal every year, not extra return. Then open the paycheck calculator with the same 6% traditional deferral to see the take-home trade tonight versus the balance in three decades.

What the calculator will not do

• Fund fees, target-date glide paths, or company-stock concentration.
• Vesting cliffs, after-tax mega backdoors, or net unrealized appreciation.
• Required minimum distributions or Roth conversion tax.

Limits and catch-up contributions change. Confirm annual IRS limits for the year you are funding. This is not a recommendation to buy any security.