Normalize the scenario
Use the same purchase amount and realistic payoff date. Record the loan's origination fee and fixed schedule. For the card, record purchase APR, any promotional period, minimum-payment rule, annual fee, and planned payment.
A card offers reusable capacity but can extend repayment when payment falls with the balance. A loan may impose a fixed payment that is less flexible but clearer.
- Net amount financed
- APR and promotional end
- Fees
- Required and planned payment
Model missed assumptions
Test a slower payoff, a missed promotional deadline, a variable-rate change, and one late payment if relevant. Keep utilization and access to remaining credit separate from dollar cost.
Compare the written product terms, not a generic category average.
Build both schedules month by month and explain every difference in total interest, fees, payoff date, and required payment.