401k match formula auditor for ADP payroll admins

The moment someone realizes they have this problem is usually after a payroll run that silently under-matched or over-matched employee contributions — and the only way they found out was a complaint from an employee or a year-end discrepancy. At that point, they have no audit trail, no way to replay what happened, and no clear owner: the payroll rep blames the 401k vendor, and the 401k vendor has no visibility into the payroll formulas.

The gap persists because ADP's incentive is to sell both the payroll product and the retirement product separately, each with its own support silo. The buyer (an HR director or CFO) signed contracts with both, but the user (a payroll admin) gets stuck in the middle with no escalation path. ADP has no structural reason to build a cross-system debugger that would expose how often these formulas break.

What admins describe is specific: 'Fixing issues with formulas for estimating 401k matches can create additional problems with other formulas.' There's no way to test a match formula change in isolation before it touches a live payroll run. And there's no log that shows which formula version was active during which pay period, so when something is wrong, you're reconstructing it from memory and exported CSV files.

This is a business and not a feature because the formula miscalculation problem recurs every single payroll cycle — it doesn't happen once. A company with 200 employees running biweekly payroll has 26 opportunities per year to match incorrectly, and each error creates legal exposure under ERISA if it's not caught and corrected within a specific window. The cost of not having this isn't just admin frustration — it's potential plan disqualification or corrective contribution filings.

What to build

Build a read-only connector that pulls ADP Workforce Now payroll deduction records and 401k plan contribution records via their APIs, reconciles them pay-period by pay-period against the employer match formula on file, and flags any period where the calculated match diverges from what was actually funded — with a plain-English explanation of which formula variable caused the gap.

Where to start

Start with companies using ADP Workforce Now paired with a specific mid-market 401k provider like Guideline or Human Interest, where both sides have reasonably accessible APIs and the employer match formula is standard enough that you can build a reliable parser without handling every edge case on day one.

The hard part

ADP's API access for payroll deduction data is gated behind partnership agreements and varies by product tier, so the first paying customer may require a manual CSV import workflow that you have to hide and then deprecate once you get proper API access — which means your first version is operationally messy and hard to scale.

How it makes money

Annual subscription per company, priced by employee count — roughly $50–150/month for sub-200 employees, scaling up. One-time setup fee to configure the match formula logic for each plan.