Loan sharks quote interest by the week because it sounds small. This calculator converts a weekly rate into what it actually costs: the total you will hand over, what you will still owe afterward, and what the same loan would cost from a legal lender. The defaults show the classic arrangement, $500 at 20 percent per week.
Assumes interest-only payments, the standard loan shark structure. Miss a week and most lenders add it to the principal, so real totals run higher.
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Here is the same math as a table, for a $500 loan at 20 percent weekly interest with interest-only payments of $100 per week:
| Time paying | Interest paid | Still owed | Credit union PAL total for comparison |
|---|---|---|---|
| 12 weeks | $1,200 | $500 | $579, and the debt is gone in 12 months |
| 26 weeks | $2,600 | $500 | |
| 52 weeks | $5,200 | $500 |
What to do with these numbers
If you are considering an informal loan, this is the price. The same money is available legally through the options in alternatives to loan sharks, most of them at a fiftieth of the cost. If you are already paying rates like these, you may not legally owe what the lender claims: start with how to get out of loan shark debt and the free counselors on our debt help page. The mechanics behind the math are explained in loan shark interest rates.
Illustrative math only, not a quote or advice. Credit union comparison assumes a 12 month payday alternative loan at the 28 percent federal cap. Last reviewed August 2026.