Line of Credit Interest Calculator
Estimate your billing-cycle interest, ending balance, and payoff timeline. This calculator uses a daily interest method and can estimate average daily balance if you do not know it exactly.
Note: If average daily balance is not entered, this tool estimates it from beginning and ending balances. Actual lender methods can vary.
How line of credit interest is calculated
A line of credit (personal, business, or HELOC) usually charges interest on the amount you actually borrow, not the full approved limit. Most lenders use a daily periodic rate based on your annual percentage rate (APR).
Interest = Average Daily Balance × (APR ÷ 365) × Days in Billing Cycle
If your balance changes during the month because you draw more or make payments, your average daily balance changes too. That is why two people with the same APR can pay different amounts of interest.
What this calculator helps you estimate
- Daily interest rate based on your APR
- Billing-cycle interest charge
- Estimated ending balance after interest
- Credit utilization if you include your limit
- Payoff time and total projected interest for a chosen monthly payment
Inputs explained
Beginning balance
This is the amount you owe at the start of the billing cycle.
New draws/charges
Any additional money you borrow during the cycle. For a business line of credit, this might include payroll, inventory, or operating expenses.
Payments/credits
Payments reduce your principal and therefore reduce future interest. Earlier payments usually save more interest than end-of-cycle payments.
APR and days in cycle
APR sets the annual cost of borrowing. The number of days in the cycle affects how much interest accrues before your statement closes.
Average daily balance override
If your statement already shows average daily balance, entering it directly gives a better estimate than using the built-in approximation.
Example scenario
Suppose you start at $5,000, borrow another $500, pay back $300, and your APR is 12.5% on a 30-day cycle. Your balance generally trends upward during the month, so interest is charged on an average amount close to that range, not just the opening balance.
Small changes can have a meaningful impact:
- Paying $300 earlier can lower average daily balance and interest.
- Reducing new draws by $100 lowers both interest and utilization.
- Increasing monthly payoff from $250 to $350 can cut total interest materially over time.
Tips to reduce line of credit interest
- Make payments earlier in the cycle, not only on the due date.
- Avoid carrying high utilization close to your credit limit.
- Automate principal payments when cash flow is strong.
- Refinance or negotiate APR if your credit profile has improved.
- Use draws strategically and repay short-term usage quickly.
HELOC and business LOC notes
HELOC interest
Home equity lines often have variable rates tied to an index. If rates move, your interest cost changes even if balance does not.
Business line of credit interest
Some lenders may charge maintenance fees, draw fees, or minimum finance charges. This calculator focuses on periodic interest, so include fees separately for a full borrowing-cost picture.
Frequently asked questions
Is this exact to my lender statement?
It is a strong estimate, especially if you provide average daily balance. Exact statement interest depends on lender timing rules, compounding method, and fee structure.
What if my monthly payment is too low?
If your payment does not exceed monthly interest, balance can grow instead of shrink. The calculator flags this so you can test a higher payment.
Should I use APR/12 or APR/365?
Many lines of credit use a daily rate (APR/365), then multiply by days. For long-run payoff estimates, monthly compounding is a practical projection approach.
Educational use only. This is not legal, tax, or financial advice.