Tax Checklist for Starting a New Job

By Tom, CPA · Updated October 27, 2026

Part of: Tax Planning

TL;DR: Set your W-4 for all household jobs, enroll to get the full match, and remember the $24,500 401(k) limit is per person across employers. Elect HSA or FSA benefits, learn your equity pay rules, and claim any excess Social Security from two employers on your return.

Educational only, not tax, legal, or investment advice. Examples are illustrations, not predictions. Rules and limits change; verify current figures and talk to a qualified professional about your situation.

The tax code is 4 million words long, and your new employer's onboarding portal will ask you to make decisions about roughly 400 of them in one afternoon, between watching a harassment training video and picking a laptop. Most people click through. This checklist is for doing it on purpose. Figures are for 2026.

CPA Warning Label: Excess 401(k) deferrals must be fixed by April 15 to avoid double taxation, and an 83(b) election has a firm 30-day deadline. Check both before year-end.

Before your first paycheck

• Fill out Form W-4 carefully. If you or your spouse have two jobs, use the IRS Tax Withholding Estimator or the multiple-jobs worksheet. Default withholding assumes this is your only job, which often under-withholds dual-income households.
• Check your state form. Many states have their own withholding certificate. If you moved, update your address and state.
• Negotiate timing of a signing bonus. A signing bonus is wages, usually withheld at 22% federal. If you are joining late in the year after a high-earning stretch, January payment may land in a lower bracket. See how bonuses are taxed.
• Understand clawbacks. Repaying a signing bonus in a later year has awkward tax treatment, so read the terms before you spend it.
• Relocation pay is taxable. Moving expense reimbursements are wages for non-military employees, and the deduction for moving costs is gone permanently. Some employers gross up the payment to cover the tax; ask.

Retirement plan enrollment

• Enroll and capture the full match. An unclaimed match is a pay cut you chose. Check the match formula and whether it is calculated per paycheck or trued up at year-end.
• Track the annual limit across employers. The 2026 employee deferral limit is $24,500 per person, not per plan, plus $8,000 catch-up at 50+ or $11,250 at ages 60-63. Your new employer does not know what you contributed at the old one. Over-contributing creates an excess deferral that must be withdrawn by April 15 of the next year to avoid double taxation.
• Roth catch-up rule. From 2026, if your prior-year FICA wages from the employer exceeded $150,000, catch-up contributions must be Roth.
• Check vesting. Matches may vest over several years. See employer match vesting.
• Handle the old 401(k). Leave it, roll it to the new plan, or roll to an IRA. Do it as a direct rollover to avoid 20% withholding. Rolling pre-tax money into an IRA can break a future backdoor Roth because of the pro-rata rule; rolling into the new 401(k) avoids that.

Benefits elections with tax value

• HSA if you choose a qualifying high-deductible plan: $4,400 self-only or $8,750 family for 2026, plus $1,000 catch-up at 55+. Payroll contributions skip income tax and FICA. Pro-rate the limit if you were not eligible all year, or use the last-month rule with its testing period.
• Health FSA: up to $3,400 for 2026, with a possible $680 carryover if the plan allows. You cannot use a general FSA and contribute to an HSA in the same year.
• Dependent care FSA: up to $7,500 per household for 2026 ($3,750 married filing separately). Coordinate with your spouse's employer.
• Commuter benefits: $340 a month for transit and $340 for parking, pre-tax.
• Group life insurance over $50,000 creates small taxable imputed income. Usually fine, just know why your W-2 shows it.
• HSA plus new employer contributions: employer HSA deposits count toward your annual limit, so subtract them before setting your payroll amount.
• Disability insurance: if you pay premiums with after-tax dollars, benefits are tax-free. Pre-tax premiums mean taxable benefits.

Equity compensation

• RSUs are wages when they vest. Withholding at 22% is often too little. See RSU tax planning.
• ESPP: a 15% discount is a strong return. See ESPP taxes.
• Stock options: note grant type (ISO or nonqualified), strike price and expiration. ISOs can trigger alternative minimum tax when exercised.
• Restricted stock at a startup: an 83(b) election must be filed within 30 days of grant. There is no extension.

Illustration: two jobs in one year

Illustration: a single filer earns $100,000 at Job A from January through June, contributing $14,000 to the 401(k) and paying $6,200 of Social Security tax. She starts Job B in July at $200,000 a year and earns $100,000 by December.

• 401(k): she has $10,500 of room left ($24,500 − $14,000), not the $24,500 Job B's portal will happily let her elect. She sets a deferral that stops at $10,500.
• Social Security: Job B withholds another $6,200 because each employer applies the wage base separately. Her total wages of $200,000 exceed the $184,500 base, so she overpaid by ($200,000 − $184,500) × 6.2% = $961. She claims it as a credit on her 1040. It is refunded at filing, not by the employer.
• Withholding: Job B's default withholding assumes $200,000 a year from one job, which happens to be close to her actual total; no big gap. In other combinations, it can be off by thousands.

Assumptions: no other income; both employers unrelated.

Before year-end

• Save your final pay stub from the old job; it shows year-to-date 401(k), HSA and Social Security figures you will need.
• Run the IRS Tax Withholding Estimator with year-to-date pay from both jobs.
• Confirm total 401(k) deferrals across employers.
• Update beneficiaries on the new plan, life insurance and any HSA. See estate planning basics.
• If income jumped, check whether you lost Roth IRA eligibility (2026 phaseout $153,000-$168,000 single, $242,000-$252,000 joint) and consider a backdoor Roth instead.
• If a new baby or home purchase is also on the horizon, see the new baby checklist and the real estate tax checklist.
• Retirees returning to work should watch IRMAA. See IRMAA planning, and long-term care planning for benefit choices.

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