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Bank Account Economics Model

Build-your-own deposit account unit economics — model net interest income, debit interchange, monthly fees, and per-account servicing cost across checking and savings products.

Make your own copy: open in Google Sheets → File → Make a copy.

How to use it

Deposit account economics come down to three numbers most pitch decks gloss over: the yield earned on the deposit balance, the fee and interchange revenue per active month, and the fully-loaded servicing cost per account. Get those three right and the rest is arithmetic — the eventual breakeven balance threshold is just a function of them.

Key inputs to set:

  • Average deposit balance per account — what an average customer holds across the deposit products you offer
  • Yield earned on deposits — the rate at which you deploy customer balances (Fed funds rate for the simplest model; asset yield if you’re using the deposits to fund lending)
  • APY paid to customer — what you pay back (0% for most checking; 4-5% for high-yield savings competing on rate)
  • Debit transactions per active month and average ticket size — drives interchange volume
  • Net interchange rate — capped at ~0.21¢ + 0.05% per debit transaction for banks with over $10B in assets (Durbin Amendment); 1.0-1.5% for smaller banks
  • Monthly account fee, overdraft fee revenue — fee-based revenue (overdraft revenue increasingly regulated; size conservatively)
  • Per-account servicing cost — card issuance, fraud, customer support, compliance, hosting, allocated per account

The output rolls up to per-account annual net interest income, fee income, total revenue, fully-loaded cost, and net profit. A sensitivity grid at the bottom shows how net profit shifts across different deposit balance assumptions — useful for figuring out which customer segments are actually worth acquiring.

Modeling assumptions

  • Single-product simplification. Most neobanks bundle checking + savings + debit; this models one product at a time
  • Interchange revenue scales linearly with transaction count; doesn’t model spend cyclicality or seasonality
  • Inactive accounts aren’t separately modeled — assume the balance figure represents an active account
  • Overdraft fees are modeled as % of accounts × fees per occurrence; CFPB rule changes may compress this revenue stream
  • No customer lifetime modeling — outputs are steady-state annual figures, not LTV