Same card, same debt as the earlier examples: $4,100, paying $230 a month, no new charges. At 18.9% APR, paid on time, that takes 22 months and $751 of interest, $4,851 total.
Cards don't all charge 18.9%. A store card or a rate hike can put the same balance at 24.99% or 29.99%. Same balance, same payment — only the rate changes. Here is what it costs.
18.9% — the baseline
- Debt-free in 22 months.
- Total interest: $751. Total paid: $4,851.
24.99% — the same debt, one rate hike later
- Debt-free in 23 months.
- Total interest: $1,078. Total paid: $5,178.
- Difference vs baseline: 1 extra month and $327 more interest.
29.99% — the penalty-rate end of the range
- Debt-free in 24 months.
- Total interest: $1,395. Total paid: $5,495.
- Difference vs baseline: 2 extra months and $644 more interest.
The payment never changed. The balance never changed. The rate alone nearly doubles the interest: $751 to $1,395.
The smaller payment gets hit harder
At $130 a month instead of $230:
- At 18.9%: 44 months, $1,612 of interest.
- At 24.99%: 52 months, $2,645 of interest — 8 more months and $1,033 more interest.
The lower the payment, the more of each payment is interest, and the more a higher rate stretches the payoff. That is the same mechanism as the minimum-payment piece: a small payment mostly feeds the rate.
Can a slightly bigger payment undo a rate hike?
At 24.99%, paying $235 a month instead of $230 gets you back to 22 months — but the interest is still $1,048, about $297 more than the 18.9% baseline. The extra $5 a month buys back the month; it does not buy back the rate. Only a lower rate does that, which is why the 0% balance-transfer piece exists.
Interest-only, for scale
Paying only the interest each month, the balance never moves:
- At 18.9%: $64.58 a month, forever.
- At 24.99%: $85.38 a month, forever.
- At 29.99%: $102.47 a month, forever.
That is the monthly price of standing still at each rate.
The honest notes
- The free calculator linked below doesn't have an APR switch; these numbers were run with the same model by hand, same assumptions as the earlier articles, so the baseline matches.
- Rates here are illustrative — check the rate on your own statement, not the one in this article. The direction holds at any balance: a higher rate costs more months and more interest at the same payment, and the gap grows as the payment shrinks.
- This is arithmetic on one example, not advice.
Run your own numbers
Try the baseline on the free calculator: https://alapha888.github.io/irregular-income-debt-baseline/
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