Buy Now, Pay Later checkout buttons make it trivial to split any purchase into a handful of installments — but nothing stops a shopper from opening several plans across different providers at once, since BNPL lenders rarely share data with each other or with traditional credit bureaus. This simulator advances week by week: new installment plans originate at a controllable rate, each stacking its own tower of payments beside the others, and every week's total burden is paid out of a fixed disposable income, oldest obligation first. Watch what happens when the queue outgrows the income — missed installments roll forward with a late fee attached, compounding into the next week's burden and pushing the live stacking-risk score from a manageable blue-and-teal skyline into a red delinquency spiral.