How Business Line-of-Credit Interest Works

Direct answer: on a business line of credit you pay interest only on the amount you have drawn and still owe, not on your total approved limit. Interest usually accrues daily on the outstanding balance and is billed monthly, so a $100,000 line with a $20,000 balance charges interest on the $20,000 only. Repay principal and the next interest charge shrinks the same day; re-draw and it climbs again. That "pay for what you use" structure is the defining difference between a revolving line and a term loan, where interest is fixed to the full amount borrowed up front. In the revenue-based and MCA marketplace most small businesses actually shop, approval leans more on your bank deposits than on your credit score, minimums start around $10,000, applicants with a FICO of 500 or higher are often considered, and decisions commonly land in 24 to 48 hours.

The Core Rule: You Pay for What You Draw

A business line of credit works like a reusable reservoir of cash. The lender approves a maximum limit, but no interest begins until you pull funds. The moment you draw, that amount becomes your outstanding balance, and interest accrues on that figure alone. The unused portion sits available and interest-free, though it may carry a small maintenance or unused-line fee covered below.

This is the practical difference from a term loan. Take a $75,000 term loan and you owe interest on all $75,000 from day one. Open a $75,000 line and draw $15,000 and you owe interest on $15,000. Draw another $10,000 next month and your interest base becomes $25,000; pay $20,000 back and it drops to $5,000. The balance revolves, and so does the interest. If you want the full picture of how revolving credit is structured, priced, and qualified for, read the business line of credit guide.

Because interest tracks the balance day by day, timing matters. Drawing late in a billing cycle and repaying early in the next can meaningfully reduce what you pay compared with carrying the same balance for a full month.

How the Interest Is Actually Calculated

Most business lines use daily accrual. The lender converts your annual rate into a daily rate, multiplies it by your outstanding balance, and adds that to a running total each day. At the end of the cycle, the accumulated daily interest becomes your charge for the month.

The common formula is:

Daily interest = Outstanding balance x (Annual rate / 365) x Number of days at that balance

Consider a simple case. Carry a $20,000 balance for a full 30-day month at an example annual rate of 24%:

• Daily rate: 24% / 365 = about 0.0658% per day
• Daily interest: $20,000 x 0.000658 = about $13.15 per day
• Monthly interest: $13.15 x 30 = about $395

Because accrual is daily, any principal payment mid-cycle lowers the balance used for the remaining days. That is why paying down early saves money even within a single month, and it is a genuine structural edge over fixed-schedule products like a term loan or an advance.

Worked Example: Interest as the Balance Moves

The table below shows how interest tracks a balance that changes during a month, using an example 24% annual rate (a daily rate of roughly 0.0658%). Figures are rounded and shown for illustration only, not a quote.

Had the full $30,000 sat untouched for all 30 days, interest would have been roughly $592. Paying principal down during the cycle cut the charge by about $184 here. The lesson is not the exact number, which will differ for every business, but the mechanic: a revolving line rewards fast repayment in a way a fixed-term product cannot.

How Repayment Hits Your Weekly Bank Balance

The interest math is only half the picture. What actually squeezes an operator is cash flow timing, not the annual percentage. On a traditional bank line, you typically owe an interest-only or interest-plus-principal payment once a month, so the drag on your account is a single monthly debit you can plan around.

In the revenue-based and MCA marketplace where most fast-funding lines and advances live, repayment is very different. Instead of a monthly bill, the funder debits a fixed amount from your business bank account every business day, or a set amount each week. That daily or weekly pull comes out whether Tuesday was a strong sales day or a dead one, so a slow week hits your available balance the same as a busy one. Before you draw, map the debit against your real deposit rhythm: if payroll clears on Fridays and card batches settle midweek, you need to know the balance can absorb the pull on the thinnest day, not the average day.

This is also why a payment can become unmanageable even when the business is healthy. If daily debits from one or more advances are choking the account, the fix is to lower the payment, restructuring or stacking relief so less leaves the account each day. It is never a matter of paying off, buying out, or settling the existing balance; the goal is simply a smaller daily drag so operations can breathe. For the broader mechanics of daily-debit products, see the revenue-based financing guide.

Decision Framework: When a Line Fits and When to Avoid It

A line of credit is a specific tool with a specific job. Interest structure is what makes it shine for some needs and expensive for others.

This works best when:

• You face recurring, short-term gaps such as payroll, inventory restocks, or slow-paying invoices, and you repay within weeks.
• You want to draw only what you need and pay interest on nothing else, keeping idle capital cost at zero.
• Your revenue is uneven and you value a standby buffer you can tap on short notice without reapplying.
• You can repay principal quickly to take advantage of daily accrual and keep the effective cost low.

Avoid this when:

• You need a large one-time sum you will repay slowly over years; a working capital term loan usually costs less for that.
• You would draw the full limit and let it sit, since idle drawn funds accrue interest every day for no benefit.
• Your account already carries heavy daily or weekly debits and another draw would tighten cash flow past the breaking point.
• You are chasing the lowest headline rate without modeling fees against how you actually plan to use the line.

What Underwriters Actually Look At

In the marketplace most small businesses shop, approval is driven far more by bank data than by a credit score. Underwriters are trying to answer one question: can this account comfortably support the draw and its repayment? The score matters, but the deposits matter more.

• Bank deposits and cash flow. The last three to six months of business bank statements are the centerpiece. Underwriters look at monthly deposit volume, consistency, and the average daily balance to judge whether the account can absorb repayment.
• Negative days and overdrafts. Frequent negative balances or bounced items signal thin cash flow and are the fastest way to a smaller offer or a decline.
• Existing daily or weekly debits. If other advances are already pulling from the account, that stacked obligation is weighed heavily against new capacity.
• Time in business and revenue. More months operating and steadier revenue widen the range of what a funder will extend.
• Credit profile. FICO of 500 or higher is often considered here, used as one input among many rather than a gate.

Minimums generally start around $10,000. Nothing about approval or rate is guaranteed; every offer follows a real review of your statements and profile.

Documents Needed and a Realistic Timeline

Fast funding is fast largely because the document list is short and the review is built around your bank data. Having the file ready is the single biggest thing you control on speed.

The whole path from application to money in the account often runs 24 to 48 hours when statements are supplied up front. Missing or partial bank statements are the most common cause of delay.

Interest Rate vs. APR, Variable Pricing, and the Fees Beside It

The interest rate is the raw cost of the money. The APR also captures certain fees, expressed as a yearly percentage so you can compare products on a more even footing. Because a line often carries draw and maintenance fees, its APR can sit noticeably above its stated rate. Two lines can advertise the same rate yet cost very different amounts once fees are counted.

Many bank-style lines carry variable rates set as the Prime Rate plus a margin. A rate quoted as "Prime + 6%" equals whatever Prime is at the time plus six points, so if Prime rises during your repayment period, your charges rise with it even if your balance is unchanged. Some marketplace products instead quote a simple periodic or factor-style cost rather than a traditional APR; always annualize before comparing, and never assume a low monthly figure means a low annual one.

Model your expected usage. A line you tap frequently is punished by high per-draw fees; a standby line is more affected by maintenance and inactivity charges. The cheapest headline rate is rarely the cheapest line for your pattern of use.

Common Mistakes to Avoid

The interest structure is simple, but a handful of predictable errors turn a cheap tool into an expensive one.

• Drawing the full limit "just in case." Every dollar you pull starts accruing interest immediately, even while it sits idle in your account. Draw what you need, when you need it.
• Comparing only the headline rate. Two lines at the same rate can cost very differently once draw and maintenance fees are counted. Compare on effective APR for your actual usage.
• Ignoring the daily or weekly debit. In the marketplace, repayment often comes out of your account every business day. Budgeting for a monthly bill that never arrives is how good businesses run short.
• Using a line for a long-term purchase. Revolving credit is built for short-term, recurring gaps. For a large one-time cost repaid slowly, a term product usually wins; compare against working capital options.
• Stacking without checking capacity. Adding a draw on top of existing daily debits can choke cash flow. If payments are already tight, the answer is to lower the daily drag, not to pile on more.
• Assuming a variable rate stays put. If your pricing is tied to Prime, leave room in the budget for it to move against you.