Short answer: For a company under 100 employees, the best 401(k) provider is the one that takes the most work off your desk in writing: who serves as the 3(16) plan administrator and the 3(38) investment fiduciary, how contributions get from your payroll to the plan, and what employees can invest in. This list compares 401GO, Basic Capital, Betterment at Work, Fidelity Advantage 401(k), Guideline (Gusto 401(k)), Human Interest and Vestwell on those points, using each provider’s own published materials as of November 2026. Coming from Human Interest? See Human Interest alternatives.

Basic Capital publishes this page and is one of the providers listed. Providers appear in alphabetical order, not ranked. Each fact comes from the provider’s own website or help center, checked November 10 to 11, 2026.

How we chose the criteria

The Department of Labor tells employers choosing a plan provider to compare the services each one provides, its total cost, whether services are bundled for one fee, and its security practices and audit results (DOL, Meeting Your Fiduciary Responsibilities). For a small company without a benefits team, four questions decide most of that:

1. Fiduciary roles. Does the provider take the 3(16) plan administrator role (notices, testing, filings) and offer a 3(38) investment fiduciary who picks and monitors the funds? Those are the jobs that otherwise stay with you.

2. Payroll fit. Does it connect to the payroll you already use, or will someone upload files every pay period?

3. Investments. A fixed menu, an open fund menu, or a brokerage window for employees who want more choice.

4. Plan features for growing teams. Safe harbor plans, Roth, and after-tax contributions for a Mega Backdoor Roth, which matter once you hire high earners.

Cost matters too. Ask every finalist for the total: recordkeeping, administration, advice and fund expenses, and who pays each.

At a glance

The providers

401GO

Fits: small companies that want one company to be administrator, recordkeeper and investment fiduciary.

• 401GO says it “is the TPA, recordkeeper, custodian (through our partner Matrix Trust), and 3(38) investment fiduciary all in one,” and its pricing page lists 3(16) plan administration and a 3(38) fiduciary, with an optional outside 3(38). (401GO pricing page, retrieved 2026-11-11)

• Offers a combined cash balance and 401(k) option on its higher tier. (401GO pricing page, verified 2026-11-10)

• Participant app on iOS and Android. (Apple App Store and Google Play listings, verified 2026-11-10)

• Check before you choose: after-tax contributions and a brokerage window are not listed on 401GO’s site as of November 2026.

Basic Capital

Fits: companies that want the administration handled and plan features that scale as they hire.

• Basic Capital Recordkeeping Services is the recordkeeper and serves as 3(16) plan administrator; Basic Capital handles admin, compliance testing and Form 5500 filing.

• Optional 3(38) investment fiduciary through Basic Capital Advisors LLC, a New York state-registered investment adviser, under a separate agreement; or keep your own adviser.

• Safe Harbor, Traditional and Pooled 401(k) plans; 6,000+ funds plus an optional brokerage window; Mega Backdoor Roth as a plan-level feature; Active Compliance monitors testing during the year.

• 300+ payroll integrations; most employers are live in 30 to 60 days; 25-minute average response time.

• Pricing is tailored to each plan, and we’re consistently competitive.

• Check before you choose: the brokerage window is optional per plan and is not monitored by the plan’s fiduciary.

Betterment at Work

Fits: small companies that want administration and investment selection bundled in every tier.

• Betterment says that “as limited 3(16) plan administrator” it handles “annual compliance testing (ADP/ACP, top-heavy), calculating contributions, preparing signature-ready Form 5500s,” and that it “offers a turnkey 3(38) fund lineup or supports advisors in a 3(21) or 3(38) role on an open-architecture basis.” (Betterment help center, retrieved 2026-11-11)

• Its pricing page lists 3(38) and 3(16) fiduciary services. (Betterment at Work pricing page, retrieved 2026-11-11)

• iOS and Android apps. (Betterment help center, verified 2026-11-10)

• Check before you choose: Betterment offers a Mega Backdoor Roth on Solo 401(k) plans only; its employer help center says it does not currently support non-Roth after-tax contributions.

Fidelity Advantage 401(k)

Fits: companies starting their first plan that want a large, familiar provider to take on most duties.

• Fidelity says it “performs most administrative duties as the Plan Sponsor, 3(16) and 3(38) fiduciary.” (Fidelity small business 401(k) page, retrieved 2026-11-11)

• NetBenefits app on iOS and Android. (App Store listing, verified 2026-11-10)

• Check before you choose: Fidelity Advantage 401(k) uses a fixed lineup of Fidelity funds and lists pre-tax, Roth, catch-up and rollover contributions only. Fidelity’s custom plans work differently.

Guideline (Gusto 401(k))

Fits: companies already on Gusto payroll that want a simple, low-touch plan.

• Gusto’s legal page says 3(16) plan administration is “only made available to clients who use the integration services available through Gusto’s payroll services,” and that Gusto Investment Services provides advice when 3(38) services are selected. (guideline.com legal page, retrieved 2026-11-11)

• Participants choose from a fund menu or managed portfolios; Gusto says it “does not accommodate for outside brokerages and trading of individual stocks.” (guideline.com portfolio page, retrieved 2026-11-11)

• Check before you choose: Gusto’s help center says its 401(k) plans don’t support non-Roth voluntary after-tax contributions or in-plan Roth rollovers.

Human Interest

Fits: small companies that want 3(16) support included and a wide mutual fund menu.

• Human Interest says its “3(16) Fiduciary Services are included in Human Interest’s Complete and Concierge 401(k) plans,” and that it offers “select 3(38) and 3(21) services” through Human Interest Advisors. (Human Interest financial advisors page, retrieved 2026-11-11)

• Enrollment webinars and onboarding in English and Spanish. (Human Interest pages, verified 2026-11-10)

• Check before you choose: “We don’t support voluntary, after-tax contributions at Human Interest.” Asked whether it has an app, its FAQ says: “Not yet, but our website is mobile-friendly.” (Human Interest learn articles, retrieved 2026-11-11)

Vestwell

Fits: small companies that want bundled administration and multilingual participant support.

• Vestwell says employers “can get reliable recordkeeping, reporting, plan tracking, government form filing, 3(16) fiduciary services, and compliance support all in one place,” with 3(16) and 3(38) oversight. (Vestwell retirement plans page, retrieved 2026-11-11)

• Account management in 18 languages on desktop and mobile. (vestwell.com, retrieved 2026-11-11)

• Check before you choose: Vestwell’s help center says a Mega Backdoor Roth “isn’t available yet, but it is coming soon” (updated September 10, 2026). Its brokerage window is through Schwab PCRA.

Questions to ask every finalist

1. Which fiduciary roles do you take, and where is that written in the service agreement?

2. What is the total annual cost, and which parts come out of employees’ accounts?

3. How do contributions get from our payroll to the plan, and who fixes a mismatch?

4. Who holds plan assets, and may we see your latest SOC reports?

5. How long until we are live, and what do you need from us?

Our guide on how to evaluate a 401(k) provider goes deeper. If you are a venture-backed company, see the best 401(k) plans for startups and Basic Capital for startups; growing past 50 people, see Basic Capital for scale-ups. Planning a match? The safe harbor 401(k) page explains the formulas, and our provider comparisons go head to head.

References

Competitor sources are listed as plain text.

• U.S. Department of Labor, EBSA. (2021, September). Meeting your fiduciary responsibilities. https://www.dol.gov/sites/dolgov/files/ebsa/about-ebsa/our-activities/resource-center/publications/meeting-your-fiduciary-responsibilities.pdf

• 401GO. (n.d.). Pricing. Retrieved 2026-11-11.

• Betterment. (n.d.). What fiduciary roles does Betterment play? Retrieved 2026-11-11.

• Betterment. (n.d.). Betterment at Work pricing. Retrieved 2026-11-11.

• Fidelity Investments. (n.d.). Small business 401(k). Retrieved 2026-11-11.

• Gusto / Guideline. (n.d.). Legal. Retrieved 2026-11-11.

• Gusto / Guideline. (n.d.). Aggressive portfolio (FAQ: Can I trade individual stocks?). Retrieved 2026-11-11.

• Human Interest. (n.d.). Financial advisors. Retrieved 2026-11-11.

• Human Interest. (n.d.). What is an after-tax 401(k)? Retrieved 2026-11-11.

• Human Interest. (n.d.). Common 401(k) questions. Retrieved 2026-11-11.

• Vestwell. (n.d.). Retirement plans. Retrieved 2026-11-11.