Consumer Credit Math: Credit Cards, APR, Minimum Payments & BNPL

What you'll build

What you will be able to do

Each lab ends with a concrete result that you build yourself and the checker confirms, cell by cell.

• Turn the APR into a daily rate, weight every balance by the days it lasted and calculate the interest for one statement cycle.
• Flag every month in which the full statement balance was paid, charge interest only when the grace period is lost and count what the partial payments cost.
• Build a 24-month minimum-payment schedule, see how much of it is interest, chart the balance and compare it with a fixed payment.
• Rank three debts for both strategies with RANK, roll each cleared payment into the next debt with FV and NPER, and measure what the order costs in interest.
• Price a 0% balance transfer: the fee, what is left when the intro period ends, the interest after it, and the net saving against staying put.
• Charge capped late fees on a pay-in-4 plan, read it as cash flows and turn two small fees into an effective annual rate with IRR.
• Size a personal loan with an origination fee, find its payment and true APR, and compare its total cost with carrying the same amount on a card.
• Calculate utilisation per card and overall, score it from a band table, combine weighted factors into a toy score and chart which card is maxed out.