{
  "methodologyVersion": "1.0",
  "studyId": "extra-payment-25-increments",
  "title": "How Every Additional $25 Changes Credit Card Payoff Time",
  "engine": "src/assets/engines/fixed-apr-payoff.js",
  "engineVersion": "1.0.0",
  "balances": [
    1000,
    2500,
    5000,
    7500,
    10000,
    12500,
    15000,
    20000,
    25000,
    30000
  ],
  "aprs": [
    9.99,
    12.99,
    15.99,
    18.99,
    21.99,
    24.99,
    27.99,
    30.99,
    32.99,
    34.99
  ],
  "baselinePaymentRatesPct": [
    2,
    2.5,
    3,
    4,
    5,
    7.5
  ],
  "extraPayments": [
    25,
    50,
    75,
    100,
    125,
    150,
    175,
    200,
    225,
    250,
    275,
    300,
    325,
    350,
    375,
    400,
    425,
    450,
    475,
    500
  ],
  "maxMonths": 1200,
  "moneyModel": "integer_cents_round_half_up",
  "percentageRule": "Percentage fields are derived from integer months or integer cents with exact rational arithmetic and rounded half-up to six decimal places.",
  "quantileRule": "The 25th and 75th percentile bands sort the eligible values and use linear interpolation at position (n - 1) * q; when the position falls between two observations, the result is interpolated proportionally between them.",
  "paymentRule": "The baseline monthly payment is calculated once as the stated percentage of the starting balance, rounded to cents, and remains fixed. The additional payment is added to that fixed payment starting in month 1 and remains fixed until payoff.",
  "interestRule": "Monthly interest equals beginning balance multiplied by APR divided by 1200, rounded to the nearest cent using round-half-up before the payment is applied.",
  "nonPayoffRule": "If rounded monthly interest is greater than or equal to the intended payment while a positive balance remains, the path is classified as non_amortizing. A path that reduces principal but does not reach zero within 1,200 months is classified as horizon_exceeded.",
  "weightingRule": "Every defined combination receives equal weight. The grid is an analytical design and is not weighted to represent the distribution of real cardholders, balances, APRs, or payments."
}