Evidence-first money workflow · Personal Money
Credit Card Interest and Fee Audit
Reproduce daily or average-daily-balance credit card interest and compare reported fees with agreement-based expected amounts and evidence.
- 1Prepare
- 2Analyze
- 3Review and export
Prepare the evidence
Paste the documented CSV schema or choose a local CSV file. Nothing is sent to Nirmion.
Review the analysis
Summary metrics lead back to the rows that support them.
Method and interpretation
How to use Credit Card Interest and Fee Audit
Use this audit after a credit-card statement reports interest or fees that need a transparent reproduction. It supports one-day balance rows and average-daily-balance summaries, keeps balance categories separate, and compares fees with user-entered expected amounts. The output is designed to prepare questions and evidence, not to decide that an issuer made a legal or billing error.
Prepare the input
For each interest category, provide method, balance basis, APR, days, and reported interest. Daily rows represent exactly one day. Average-daily-balance rows can represent a statement-cycle day count. Add optional fee rows with the reported amount, the expected amount from your agreement or disclosure, and a note. Separate purchases, cash advances, transfers, and promotional balances when rates differ.
Check the worked example
The example models thirty days on a USD 1,000 average daily purchase balance at 24% APR and one daily cash-advance balance. The entered reported interest matches the rounded model. One fee matches its expected amount, while another differs by fifty cents and remains an action row.
Read the evidence
Compare modeled and reported interest by category before reviewing the net total. A difference can come from compounding, leap-year convention, transaction posting time, grace-period status, a balance definition, rounding level, or an incorrect input. Fee differences remain separate because interest and fees have different evidence. Use the note column to record the disclosure or calculation you relied on.
Calculation method
Modeled interest = balance × APR ÷ 365 × days, rounded to the nearest minor unit for each supplied row. APR accepts two decimal places. Reported difference = reported interest − modeled interest. Fee difference = reported amount − expected amount. The unexplained total adds both signed differences.
Review CFPB’s average daily balance and daily rate explanation
Questions this workflow helps answer
Use these questions to confirm that this tool matches the task you need to complete.
- How can I reproduce a credit card interest charge from APR, balance, and days?
- Does my reported card interest match an average-daily-balance calculation?
- Which credit card fees differ from the amounts documented in my agreement?
Limits and decision boundary
Issuer agreements may compound daily, use 360 or 365 days, include prior interest, assign fees to a balance, apply grace periods, use separate promotional rates, or round at another level. This model cannot establish a billing violation. Verify the agreement, statement’s balance-subject-to-interest value, and issuer explanation.
Common mistake
Do not use the closing statement balance as average daily balance unless the statement identifies it that way. A single end-of-cycle balance can materially misstate interest.
Your pasted values and selected CSV files are processed in this browser tab. This workflow does not connect to a bank, save a budget, or provide financial, tax, legal, or investment advice.
Questions about this workflow
Why must a daily row have one day?
It preserves the meaning of daily evidence. Use one row per day or use average_daily_balance with the documented number of cycle days.
Can I combine purchase and cash-advance balances?
Only when the same APR and balance method apply. Separate categories are safer because statements can apply different rates and rules.
What should I do with a difference?
Recheck inputs and disclosures, then ask the issuer for its calculation when needed. The tool does not determine legal liability or resolve a dispute.