How Is Line of Credit Interest Calculated?

How do I calculate interest on a line of credit?

If you have asked how do I calculate interest on a line of credit, the answer starts with daily balances. Canadian banks and credit unions accrue interest each day on whatever you owe that night. The annual rate is divided by 365 (some institutions use 366 in leap years) to get a daily factor. Multiply each day's balance by that factor and sum across your statement period — that total is your interest charge for the month.

Unlike a fixed installment loan, a LOC balance changes whenever you spend, repay or transfer. Two months with the same average balance can still produce different interest if spending was front-loaded versus back-loaded. This educational calculator shows the mechanics with either a steady balance or an illustrative varying pattern so you can see how daily accrual adds up.

How is line of credit interest calculated by banks?

How is line of credit interest calculated in practice? Most institutions use average daily balance: add each day's ending balance, divide by days in the period, multiply by annual rate divided by 365. Purchases increase your balance immediately; payments reduce it when credited. There is no grace period on interest like some credit cards offer — from dollar one, drawn funds accrue.

Variable-rate LOCs reset when prime changes. Your daily factor updates with the new annual rate on the effective date stated in your agreement. Fixed-rate personal LOCs are rare; most Canadian products float. Check your statement for the exact rate applied each period.

Average daily balance vs simple interest

Simple daily interest on a constant balance is the easiest case: monthly interest ≈ balance × (annual rate ÷ 100) ÷ 365 × days in month. The table above walks through each day so you can verify the sum. When balances fluctuate, only the average daily balance method matches your statement — enter transactions day by day for precision, or use a single average if you want a quick estimate.

HELOCs compound the same way as unsecured lines, though rates are usually lower because of home security. Business operating lines follow identical maths with potentially different rate margins and fees.

Reducing LOC interest charges

Pay early in the billing cycle when possible — every day at a lower balance saves interest. Sweep surplus cash against the line before month-end. Avoid carrying a high balance while parking cash in a low-interest chequing account; offset mortgages are different, but standard LOCs do not offset. Consolidating high-rate card debt into a lower-rate LOC cuts the daily factor applied to the same spending.

Use this calculator to test scenarios: if I keep $10,000 drawn at 10%, how much interest is one month? What if I pay $2,000 mid-month? Manual day-by-day entry in a spreadsheet plus this tool's breakdown builds intuition faster than reading alone.

Statement reconciliation tips

Compare your calculated monthly interest to line 3 on your paper or PDF statement. Small differences may reflect leap years, promotional rates, or fees coded as interest. Large gaps mean balances or rates differ from your assumptions — download transaction history and rebuild daily balances for that period.

Understanding how line of credit interest is calculated turns a mysterious charge into something you can forecast and reduce. Keep this page handy when weighing LOC versus term loan structures for your next major expense in Canada.

Tips before you apply