What’s a file?
Credit card interest calculator: what will this really cost?
Put in what you’re buying and what you can pay each month. See how long it takes and what it really costs, or how to pay $0.
Your answer
Updates as you typePut in the price and what you can pay each month.
Decode your statementTap each box: what it means and which one to pay
A sample statement with Jordan’s numbers. Tap any box to see what it means. The dates are examples.
New balance (statement balance)
What you owed on the closing date. Pay this in full by the due date = $0 interest.
Statement-date utilization checkerHow much to pay before your statement closes
Your balance is usually reported on the statement closing date. What you owe that day is what the credit bureaus see.
- Card 1
Add your card limit and current balance.
Keep it under 30% (CFPB). People with exceptional scores average single digits (Experian).
Cash advance costThe ATM button: a fee, then interest from day one
Add the cash amount and your card’s fee.
Lending a friend money? Use your bank account, and only what you can afford to lose.
FILE 004 · Your first-card rules · theadultfiles.com
Your first-card rules
0 of 7 checkedSources
- Federal Reserve, G.19 Consumer Credit: Commercial bank interest rate on credit card plans, accounts assessed interest: 22.15% (Q2 2026)
- Regulation Z §1026.7(b)(12): The Minimum Payment Warning on US statements, and the 3-year payment estimate
- Regulation Z §1026.5(b)(2)(ii): US statements must be sent at least 21 days before the payment due date
- CFPB: Can I withdraw money from my credit card at an ATM?: Cash advance fees, a usually higher rate, and interest from the day you withdraw
- CFPB: How do I get and keep a good credit score?: Keep your use of credit at no more than 30% of your limit; you don’t need to carry a balance
- Experian: What is a credit utilization rate?: Those with the highest scores tend to have utilization in the low single digits
- FCAC: Paying off your credit card: Minimums of typically 3% or $10; 5% in Quebec since Aug 1, 2025; the $2,000 at 18% example
- FCAC: How credit cards work: Federally regulated institutions must provide a minimum 21-day grace period
- myFICO: What’s in your credit score: Payment history 35%, amounts owed 30%, length of history 15%, new credit 10%, credit mix 10%
The formula, in the open
A month-by-month simulation, the same way a card works: interest is charged on the balance, then your payment comes off. Three paths, side by side: the minimum, your plan, and paying the statement balance in full (which keeps your grace period, so $0 interest on purchases).
US minimum: a common formula (interest + 1% of the balance, at least $35); Canada: FCAC’s typical 3% or $10, and 5% in Quebec. Minimums vary by card, so you can change the rule. Numbers only go in the link; what you’re buying never does.
- Interest each month
- = balance × APR ÷ 12 (the daily rate × 365 ÷ 12), to the cent
- Interest per day
- = balance × APR ÷ 365
- US minimum (default)
- = interest + 1% of the balance, at least $35 (or the full balance if less)
- Canada minimum (default)
- = 3% of the balance or $10, whichever is more (Quebec: 5%)
- Paid for it ×
- = total paid ÷ price
- 3-year payment (warning box)
- = the amortization payment that ends in 36 months
- Utilization
- = balances ÷ limits; pay down to report under 30% or 10%
- Cash advance
- = amount + fee before you leave the ATM, then interest from day one