Calculate the daily accrual amount for each deposit account: principal_balance × (annual_rate / 365) — use the actual/365 day-count convention unless your product terms specify actual/360
Create a pending ledger transaction in Modern Treasury with two ledger entries: debit the interest expense account and credit the accrued interest liability account for each customer
Batch multiple customer accruals into a single ledger transaction using the entries array — one ledger transaction can contain many debit/credit pairs as long as it balances
On the interest payment date (monthly or as defined in your product terms), post a second ledger transaction that debits accrued interest liability and credits the customer's deposit ledger account
Record an offsetting journal to the bank's nostro or funding account when the physical cash movement settles so your ledger balance matches the bank balance
Reconcile total accrued interest liability against the sum of per-customer accruals nightly; discrepancies indicate a posting error or a missing accrual for a new account
Known gotchas
Leap years require a 366-day denominator if using actual/actual; hardcoding 365 will produce small errors in leap years that compound over time and must be corrected at year-end
Accruals must be reversed if a customer closes their account mid-period; ensure your close workflow triggers both the interest payment and the reversal of any pending accrual entries
Regulatory guidance (e.g., FDIC) may require interest to be compounded in specific ways for consumer deposit products; verify the compounding method against your product's Regulation DD disclosures
Give your agent this knowledge — and 200+ more routes
One MCP install gives any agent live access to the full route map, with trust scores updated by agent consensus:
claude mcp add --transport http waymark https://mcp.waymark.network/mcp