Because contributing to a 401(k) plan is a tax benefit, the IRS sets both participant and plan-level limits on the benefits any individual can receive. All plans are subject to these limits, including those with a Safe Harbor provision.

The annual deferral limit, also known as the 402(g) limit, is the maximum allowable amount that a participant can personally contribute, or defer, into any plan as a salary reduction election. This limit includes all amounts deferred into any 401(k), 403(b), or SIMPLE 401(k) plan, regardless of the plan sponsor. This limit also includes both pre-tax and Roth contributions.
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The annual additions limit, also known as the 415 limit, is a combined limit of employee (salary reduction elections) and employer contributions (e.g., match and nonelective) that can be contributed during a plan year. This limit is per plan sponsor and would be combined with those in the same controlled group or affiliated service group. However, it is not combined for participants in separate plans sponsored by unrelated employers.
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Most employer contributions are expressed as a percentage of compensation (e.g., a nonelective contribution of 3% of compensation or a 100% match on deferrals up to 4% of compensation). The annual compensation limit, also known as the 401(a)(17) limit, caps the compensation that can be considered when calculating employer contributions.
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The employer deduction limit is the maximum total contributions an employer can make to the plan as a whole. Plans that exceed the deduction limit can incur substantial penalties.
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While Guideline monitors these limits with the data available, employers should also keep track of their own limits, especially when transitions take place, including when changing payroll providers or converting to Guideline from another service provider.
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You can learn more about limits and other plan compliance testing here.