Castle Biosciences CSTL Accounts Receivable, Allowance for Credit Loss

We accrue an allowance for credit losses against our accounts receivable based on management’s current estimate of amounts that will not be collected. We have elected the practical expedient under ASC Topic 326, Financial Instruments - Credit Losses (“ASC 326”) to assume that current conditions as of the balance sheet date do not change for the remaining life of our accounts receivable. Accordingly, management’s estimates are based on historical loss information adjusted for current conditions. We generally do not perform evaluations of customers’ financial condition and generally do not require collateral. Historically, our credit losses have not been significant. The allowance for credit losses was zero as of March 31, 2026 and December 31, 2025. Adjustments for implicit price concessions attributable to variable consideration, as discussed below, are incorporated into the measurement of the accounts receivable balances and are not part of the allowance for credit losses.