Defending your bad-debt reserve to your auditor

Every year-end, the same conversation: the auditor asks why your allowance for doubtful accounts is the number it is, and "it's what we've always booked" stops being an answer around the second year of CECL. The reserve is a judgment, but it's a judgment that needs a method. Here's how to defend it—or know it won't survive.

The method matters more than the number

ASC 326 (CECL) replaced the old incurred-loss model with an expected-loss one. That sounds technical until you translate it: your reserve now has to look forward, not backward. Two methods dominate for software receivables:

• Aging-based: a loss rate applied to each aging bucket—current, 1–30, 31–60, 61–90, 90+. Simple, defensible, and what most SaaS companies use.
• Loss-rate: historical write-offs divided by collections, adjusted for current conditions. More precise, harder to explain in a footnote.

Either works. What doesn't work is a flat percentage that never moves while your aging mix drifts—because the auditor can see the drift in the same report you're looking at.

The evidence that carries the number

When the reserve is questioned, three documents settle most arguments:

• Two to three years of write-off history by aging bucket, with the calculation visible
• Your current aging report, aged the same way the reserve is built
• Anything that explains a change—a big customer in distress, a shift to longer payment terms, a new channel with a weaker credit profile

Where collection activity fits

A documented collection effort is evidence of a different kind. When an account sits at 120 days with no activity, the auditor reads that as expected loss. When it sits at 120 days with a placement file, a demand, and a payment plan under negotiation, the reserve can reflect a real recovery probability instead of a guess. That distinction is why credit teams with a placement trigger carry smaller, better-supported reserves—the work behind the receivable justifies the number.

The best time to fix a reserve question is before the auditor asks it. If you have an aging book full of accounts you intend to write off but haven't, run them past a collector first—some of those "expected losses" are collectible, and the documentation from a real attempt is exactly what the reserve defense needs.