How to Set Up Section 125 Pre-Tax Deductions in Gusto

If you’re running a small to mid-sized business and managing payroll through Gusto, you might be wondering how much work is involved in setting up Section 125 pre-tax deductions. The good news: Gusto has built-in features that make this easier than ever. The honest news: you still need to understand the basics of how it works and what you need to do on your end.

This guide walks you through planning, payroll execution, and year-end reporting so you can set up Section 125 pre-tax deductions in Gusto with clearer expectations.

Primary next step: Start a Benefits Readiness Snapshot so plan-document status, Gusto deduction setup, and provider questions are organized before licensed review. Use the FICA calculator or savings estimator as secondary educational estimates only.

Why Gusto Works Well for Small Business Benefits

Gusto has become one of the most popular payroll platforms for small businesses, partly because it handles the administrative headaches of benefits. Instead of manually calculating deductions across payroll runs, Gusto’s platform lets you set up pre-tax benefits once and it applies them automatically to every paycheck.

For Section 125 specifically, Gusto recognizes that many small business owners and HR managers don’t have dedicated benefits teams. The platform bridges that gap by offering built-in benefit administration features-no separate software required. You configure the deduction amounts in Gusto, and it calculates the tax impact correctly with each payroll run.

That said, Gusto is not a substitute for a proper Section 125 plan document. It’s a tool for administering the plan, not writing it. That distinction matters, and we’ll cover it next.

Gusto’s Built-In Benefits vs. External TPA Approach

Before integrating Gusto with your Section 125 plan, understand the overall implementation process in Section 125 Implementation Guide. Here’s what you need to know about how Gusto fits into the bigger Section 125 picture:

Gusto’s role: Gusto handles payroll deductions, employee enrollment flows, and the ongoing administration of benefits you’ve already set up. It’s the “how much comes out of each paycheck” platform.

What you still need: A Section 125 plan document-the legal foundation that allows the pre-tax treatment in the first place. This document can come from either a Third Party Administrator (TPA) or, in some cases, Gusto itself (we’ll explain below).

The key insight: small businesses often think they need a full-service TPA to manage Section 125. In reality, if your plan is straightforward-health insurance premiums and maybe dependent care FSA-Gusto can handle most of the administration. A TPA becomes more critical if you have complex cafeteria plans, multiple benefit tiers, or if you need support with nondiscrimination testing (which we’ll cover later).

Step-by-Step Setup in Gusto

Step 1: Get Your Plan Document

Before you add anything in Gusto, you need a Section 125 plan document. Here’s what you have two options:

1. Gusto’s plan document service: Gusto can generate a basic Section 125 plan document for you through their platform. This is often used for straightforward scenarios: health insurance premiums, health savings accounts (HSAs), and dependent care FSA. It typically costs extra (commonly cited in the $200–$400 range as a one-time fee). Confirm current pricing and whether the document fits your plan design with Gusto and a qualified advisor — a written cafeteria plan is required under the IRC §125 framework described in IRS Publication 15-B.

2. External TPA: If you already work with a TPA or prefer their guidance, ask them to provide your plan document. Some TPAs integrate with Gusto; others don’t-but that doesn’t prevent you from using both.

Either way, don’t skip this step. The plan document is what makes the pre-tax deduction legally defensible. Gusto won’t let you set up pre-tax benefits without acknowledging that this document exists (and you’ll need to confirm it’s in place).

Step 2: Add a New Benefit in Gusto

Once the plan document is in place, here’s what the setup looks like in Gusto. This gives you a sense of how straightforward the process is, whether you’re doing it yourself or working with a TPA.

1. In Gusto, go to Benefits > Add Benefit
2. Select the type of benefit-Pre-tax health insurance deduction is the most common for Section 125
3. Name the benefit (e.g., “Health Insurance Premium - Pre-Tax”)
4. Set whether it applies to all employees or specific groups

Gusto will ask you to confirm that you have a Section 125 plan document. Say yes, and proceed.

Step 3: Set Deduction Amounts for Each Employee

This is where the real work happens. Gusto lets you either:

• Manual entry: Go into each employee’s profile and enter their individual premium deduction amount
• Bulk import: Upload a spreadsheet if you have multiple employees with different deduction amounts

Your deduction amount should match what each employee pays for their health insurance premiums (or HSA contributions, or dependent care FSA contributions-whatever you’ve included in your plan).

When configured correctly under a Section 125 cafeteria plan, Gusto generally treats the amount as a pre-tax deduction: it can reduce the employee’s taxable wages and update federal/state/FICA withholding accordingly. Confirm treatment with your payroll settings and advisor.

Step 4: Gusto’s Automatic Processing

Here’s where Gusto shines: once you’ve entered the amounts, Gusto does the math automatically on every payroll run. It:

• Reduces gross wages by the deduction amount
• Recalculates federal income tax withholding (lower taxable wages = lower withholding)
• Recalculates FICA withholding (Social Security and Medicare)
• Accounts for state income tax variations

You don’t have to think about it again unless the deduction amount changes.

Which Gusto Plan Do You Need?

Gusto offers several payroll tiers. Here’s what you need for Section 125:

• Gusto Core: Handles basic payroll but limited benefits administration. If you just want to deduct health insurance premiums, this may work.
• Gusto Plus: Includes full benefits administration, employee self-service enrollment, and integrated health insurance shopping. This is the tier most small businesses use for Section 125.
• Gusto Premium: Adds compliance and HR features; useful if you have many employees or complex benefits needs.

For most small businesses setting up Section 125, Gusto Plus is the right choice. It includes the benefits portal where employees can see and manage their deductions.

Common Scenarios: New Hires, Terminations, and Changes

New hires: Gusto’s onboarding flow includes benefits enrollment. New employees can elect their pre-tax deductions during onboarding, and Gusto applies them starting with their first paycheck. This is seamless.

Mid-year changes: If an employee needs to change their deduction amount (because their health plan changed, they had a life event, etc.), they can update it in their Gusto employee portal. The new amount takes effect on the next payroll run you specify. You can also make manual changes on their behalf.

Terminations: When an employee leaves, Gusto stops deducting their benefits. You can set an end date, and the deductions stop after their last check. Make sure to coordinate with your health insurance carrier-Gusto handles the payroll side, but you may need to update your insurance group separately.

Gusto + External TPA Integration: When You Need Both

Here’s a practical question: what if you already work with a TPA or want to add one?

Short answer: Gusto and a TPA can work together, but you have to be intentional about roles and responsibilities.

• Gusto’s job: Calculate and process deductions, administer employee contributions, generate payroll reports
• TPA’s job: Provide compliance guidance, run nondiscrimination testing, manage plan documents, help with amendments

If your TPA provides their own enrollment portal or plan administration software, you may have some duplication-but it’s manageable. Make sure your TPA knows you’re using Gusto so they don’t assume they’re handling everything.

If you’re just starting out and your plan is straightforward, you may not need a TPA at all. Gusto + a good benefits consultant (not a full TPA) is often enough for small businesses.

Limitations: What Gusto Doesn’t Handle

Gusto is powerful for basic Section 125 administration, but it has limits:

• Nondiscrimination testing: Gusto doesn’t run the annual IRS tests that ensure your plan doesn’t discriminate in favor of highly compensated employees. You’ll need a TPA for this.
• Complex cafeteria plans: If you’re offering multiple benefit tiers, limited-purpose FSAs, or dependent care FSAs with complex rules, Gusto can handle the deductions but may not support all the plan design nuances. A TPA can help here.
• Plan amendments: If you need to update your plan document (new benefit type, new eligibility rules), you’ll need to work with whoever provided your plan document (Gusto or your TPA).
• Compliance consulting: Gusto provides solid documentation and support, but it’s not a substitute for a benefits advisor who understands your specific situation.

Year-End: W-2s and Tax Filing

One of the best parts of using Gusto: it handles year-end automatically.

Gusto calculates the correct pre-tax deductions for each employee across all payroll runs and reflects them on W-2s. The employee’s taxable wages are reduced by the Section 125 deductions, which means lower federal income tax withholding.

When you file W-2s (which Gusto can do for you, or you can use another service), the pre-tax amounts are already calculated correctly. You don’t have to go back and adjust anything.

For federal filing, eligible Section 125 salary reductions typically reduce the taxable wages reported in Box 1 rather than appearing as a separate W-2 line item. Confirm current Form W-2 reporting with your payroll provider or tax professional.

Getting Started

If you’re running payroll through Gusto and want to add Section 125, here’s what to do:

1. Decide on your plan document. Will you use Gusto’s document service, or do you already have one from a TPA?
2. Make sure you’re on Gusto Plus or higher. Core tier won’t give you the benefits administration you need.
3. Set up the benefit in Gusto. It takes about 15 minutes.
4. Enter deduction amounts. This is the biggest time investment-but it’s a one-time setup.
5. Run your next payroll. Gusto applies the pre-tax treatment automatically.

You might also want to compare Gusto’s setup with other payroll providers like ADP or Paychex.

Section 125 doesn’t have to be complicated, especially if you’re using the right tools. Gusto is designed to make this straightforward for small businesses. Start with a clear plan document, set the deductions correctly, and let Gusto do the heavy lifting.

Sources

• IRS Publication 15-B (2026), Employer’s Tax Guide to Fringe Benefits — cafeteria plans under IRC §125, qualified benefits, and employer fringe-benefit tax treatment
• IRS Topic 751, Social Security and Medicare withholding rates — FICA rate components (6.2% + 1.45%) and Social Security wage-base framing
• IRS Publication 15 (Circular E), Employer’s Tax Guide — employment tax withholding context for payroll setup

Next Steps

Primary: Start a Benefits Readiness Snapshot so plan-document status, Gusto payroll setup, and provider-path questions are clear before licensed review.

Secondary estimates: FICA savings calculator · company savings estimator

If you are also tightening hire-day enrollment communication, see the new hire benefits enrollment guide.

This guide is for informational purposes and does not constitute tax, legal, payroll, or benefits advice. Gusto product features and fees change; verify current steps in Gusto Help and with a qualified advisor before implementing.