You pay interest only on the money you actually draw, never on the unused portion of your credit limit. Most lenders calculate that interest daily, using a daily periodic rate pulled from your APR, then total it up over your billing cycle. The real cost of your line depends less on the headline rate and more on how quickly you repay what you borrow and how fees stack on top.
TL;DR:
- Most lenders calculate interest based on the average daily balance, with rates derived from the APR divided by 360 or 365 days, affecting the total interest paid.
- Staggered draws and mid-cycle payments significantly change the average daily balance, resulting in higher interest costs compared to a single draw, especially when using an 8% APR over 30 days.
- Tiered interest rates range from about 3% for strong bank borrowers to over 60% for riskier online options, with SBA-backed lines averaging around 11.75%.
- Paying balances early, comparing total costs including fees, and considering secured versus unsecured options can reduce the true interest expense of the line of credit.
- Interest begins accruing immediately after drawing funds and switches from interest-only to repayment phases, which can cause payment shocks if not planned for.
Table of Contents
- How Lenders Calculate Interest on a Line of Credit
- Rate Types and Fees That Change Your True Cost
- Worked Examples: What $10,000 and $50,000 Actually Cost
- When Interest Starts and Why Timing Matters
- How to Cut Your Line of Credit Interest Costs
- Tax Implications of Interest Paid on a Line of Credit
- What 30 Years in Small Business Lending Has Taught Us About Lines of Credit
- Why Excel Capital Management Might Be Your Fastest Path to a Working Line of Credit
- Sources
- FAQ
How Lenders Calculate Interest on a Line of Credit
Every lender starts with the same basic math, even though the labels on your statement might make it look complicated. The daily periodic rate is your APR divided by a day-count convention, either 365 or 360 days, depending on what your agreement specifies. That daily rate then gets multiplied by your average daily balance and by the number of days in your billing cycle.
The formula looks like this:
Interest = Average Daily Balance × (APR ÷ 365) × Days in Billing Cycle
Lenders calculate the average daily balance by adding up your outstanding balance for every day in the cycle, then dividing by the number of days, according to Investopedia’s breakdown of how interest is charged on lines of credit. If you draw $5,000 on day one and pay down $2,000 on day 15, your daily balances shift accordingly, and the average reflects that movement rather than just your starting or ending number.
Most lines of credit use simple interest calculated fresh each cycle rather than compounding daily like a credit card typically does. Your agreement will state which method applies, along with whether unpaid interest gets added back to your principal, a process called capitalization that increases the balance you owe interest on going forward, according to LegalClarity’s explanation of line of credit interest calculations.
Before you sign anything, check two things in your contract:
- Whether the day-count convention is 365 or 360 (360 produces slightly higher effective rates)
- Whether the agreement describes simple interest or allows capitalization of unpaid balances
Pro Tip: Ask your lender directly whether interest compounds. A one-word answer here can save you from miscalculating your true borrowing cost by hundreds of dollars a year.
Rate Types and Fees That Change Your True Cost
Not all lines of credit price interest the same way, and the sticker rate rarely tells the whole story. Fixed-rate lines lock in a set APR for the life of the agreement, while variable-rate lines move with an index, typically the prime rate plus a margin your lender sets based on your creditworthiness.
Some alternative lenders skip APR altogether and use factor rates instead, a flat multiplier applied to the amount borrowed, often paired with weekly or monthly fees rather than a traditional daily accrual. These structures can obscure the real annualized cost unless you convert them yourself.
Watch for these common charges layered on top of interest:
- Origination fees, charged once when the line opens
- Draw fees, charged each time you pull funds
- Annual or maintenance fees, charged simply for keeping the line open
- Non-usage fees, charged if you draw too little
Business line of credit APRs span an enormous range, from roughly 3% for the strongest bank borrowers up to 60% or higher for riskier, fast-funded online products, with Bankrate’s Small Business Lending Survey putting Q3 2025 averages around 6.99% to 7.91% depending on whether the rate was fixed or variable. SBA-backed revolving lines have carried starting rates near 11.75%, per the same Bankrate coverage, giving you a useful public anchor when comparing private offers.
Worked Examples: What $10,000 and $50,000 Actually Cost
Numbers make this easier to trust than formulas alone. Here are two scenarios you can reproduce in a spreadsheet in under five minutes.
- $10,000 draw, 30 days, 8% APR, 365-day convention. Daily periodic rate = 8% ÷ 365 = 0.0219%. Interest = $10,000 × 0.000219 × 30 = $65.75 for the month.
- $50,000 staggered draws with a mid-cycle payment. Say you draw $30,000 on day 1, another $20,000 on day 10, then pay $15,000 on day 20 of a 30-day cycle. Your average daily balance works out to roughly $43,500 (9 days at $30,000, 10 days at $50,000, 11 days at $35,000, weighted and averaged). At 8% APR, interest = $43,500 × 0.000219 × 30 ≈ $285.87.
| Scenario | Average Daily Balance | APR | Days | Interest Owed |
|---|---|---|---|---|
| $10,000 single draw | $10,000 | 8% | 30 | $65.75 |
| $50,000 staggered draws | $43,500 | 8% | 30 | $285.87 |
Switching to a 360-day convention instead of 365 raises the daily rate slightly and increases interest owed by roughly 1.4% on the same balance. To reproduce these numbers yourself, drop the average daily balance, APR, and cycle length into a basic spreadsheet formula: balance times (APR divided by day count) times days.
When Interest Starts and Why Timing Matters
Interest typically begins accruing the day you draw funds, not the day you receive your statement, according to LegalClarity’s timing explanation. A payment that posts a few days after you submit it still counts as unpaid for those extra days, which raises your average daily balance for that cycle.
Many lines also shift from an interest-only draw period into a repayment period where you owe principal plus interest, and that transition often creates real payment shock if you weren’t planning for it.
Check your statement for three things:
- The exact start and end dates of your billing cycle
- The line labeled “finance charge” or “interest charge” for the period
- Which day-count convention the agreement uses
Pro Tip: Set payment reminders two to three days before your billing cycle closes, not on the due date. Posting delays are the single most overlooked reason borrowers pay more interest than they expect.
How to Cut Your Line of Credit Interest Costs
Reducing interest starts with a simple habit: borrow only what you need right now, and repay it as fast as cash flow allows, since NetCredit notes that your average daily balance, not your credit limit, drives the charge.
A few moves make a measurable difference:
- Pay down balances before your billing cycle closes rather than on the due date, which lowers that cycle’s average daily balance
- Compare offers on total cost, not headline rate. Convert one-time origination or draw fees into an annualized figure so you’re comparing apples to apples
- Check your credit profile before applying, since stronger credit typically unlocks lower margins over prime
- Ask whether a secured line is available if you have collateral to offer, since secured lines often carry lower rates than unsecured ones
Pro Tip: Run the annualized-fee math on any factor-rate or flat-fee product before comparing it to a traditional APR line. What looks cheaper on the surface sometimes isn’t once fees are converted to a yearly rate.
Tax Implications of Interest Paid on a Line of Credit
Whether you can deduct interest on a line of credit depends almost entirely on what you did with the money, not on the type of credit product itself. The IRS generally allows business owners to deduct interest on funds used for ordinary and necessary business expenses, such as inventory, payroll, or equipment, but personal draws from the same line typically aren’t deductible.
That distinction matters if you run a business line of credit through a mix of business and personal expenses. Mixing uses on one account makes it harder to substantiate the business portion at tax time, and lenders don’t track your intent for you. Keep a simple log of what each draw funded, ideally tied to receipts or invoices, so your accountant can allocate interest correctly between deductible and non-deductible use.
Interest on a personal line of credit used for personal expenses, like a vacation or debt consolidation, generally isn’t deductible under current federal rules. If you used a home equity line of credit, different rules apply depending on whether the funds went toward home improvements versus other purposes, and those rules have shifted more than once in recent years.
None of this is a substitute for a conversation with a tax professional who can see your full financial picture. The stakes are high enough, and the rules specific enough to your situation, that a general guide can only point you toward the right questions to ask.
What 30 Years in Small Business Lending Has Taught Us About Lines of Credit
Some lenders have spent more than three decades in business lending, and the pattern that repeats most often isn’t about rates. It’s about businesses opening a line of credit for the wrong reason, or at the wrong time, and then feeling the interest cost as a surprise rather than a plan.
A line of credit fits best when your need is recurring and unpredictable in timing, covering seasonal payroll gaps, restocking inventory ahead of a busy season, or bridging a slow receivables cycle, as explained by Commercial Investments with The Carteret Group | Luxury Real Estate in North Carolina. It fits less well for a single large, predictable purchase, where a term loan or equipment financing often carries a lower total cost.
Before you apply anywhere, pull your recent financials, estimate how much you’d actually draw in a typical month, and compare full APR-plus-fee costs across at least two offers side by side.
— Excel
Why Excel Capital Management Might Be Your Fastest Path to a Working Line of Credit
Speed changes what a line of credit can do for your business. If a payroll gap or an inventory opportunity can’t wait for weeks of underwriting, Some lenders fund approved applications quickly, treating every application with the same review process regardless of business size.
That speed matters most when you’re comparing a bank’s lower advertised rate against the real cost of waiting three to six weeks for approval. Excel Capital Management works across a range of products, including business lines of credit, so you can compare APR, fees, and draw terms against what you’ve calculated using the formulas above before committing to anything. If your business needs fast, transparent access to a revolving line of credit without a drawn-out bureaucratic process, start by requesting a quote and comparing the real numbers side by side.
This article is general information, not a substitute for advice from a qualified financial advisor. Consult a qualified financial professional about your own circumstances before acting on anything here.
Sources
- Average Business Line of Credit Interest Rates | Bankrate
- How Interest Is Charged on Lines of Credit | Investopedia
- How Is Interest Calculated on a Line of Credit? | LegalClarity
- How does interest on a line of credit work? | NetCredit Blog
FAQ
What is the current interest rate on a line of credit?
Business line of credit rates typically range from about 3% for the strongest borrowers up to 60% or higher for riskier products, with recent averages around 6.99% to 7.91% for new bank-issued lines.
What is interest on a line of credit?
It’s the cost charged on the amount you’ve actually drawn, calculated daily using a periodic rate derived from your APR, and applied only to your outstanding balance rather than your full credit limit.
What is the monthly payment on a $50,000 line of credit?
It depends on your average daily balance and APR rather than the full limit; a $50,000 line with staggered draws averaging around $43,500 at 8% APR generates roughly $286 in interest for a 30-day cycle, plus any principal repayment your agreement requires.
How much interest will I pay on a $10,000 line of credit?
At 8% APR over a 30-day cycle with the full $10,000 outstanding the entire time, you’d owe about $65.75 in interest, using the daily periodic rate method most lenders apply.
