The formula
A business loan payment is one formula, not a negotiation: the monthly payment M = P × r × (1+r)^n ÷ ((1+r)^n − 1), where P is the loan amount, r is the monthly rate (the annual rate divided by 12) and n is the number of monthly payments (the term in years times 12). The total paid is the monthly payment times n, and the total interest is the total paid minus the loan. Whichever of the three numbers you are solving for, the same seven steps give the answer — and the business loan calculator runs them for you.
Step 1 — Gather the three numbers
Start with the three numbers the payment depends on: the loan amount, the annual rate, and the term in years. Our worked example uses a $50,000.00 loan at 7.5% over 5 years — a round, typical small-business loan. The rate a lender quotes is usually an APR, so use the number on the quote, not the number in the headline. Most small-business loans run 3–10 years, with SBA loans sometimes running longer. Write the three numbers down before you touch a calculator: $50,000.00, 7.5%, 5 years.
Step 2 — Turn the annual rate into a monthly rate and the term into payments
Divide the annual rate by 12 to get the monthly rate, and multiply the term in years by 12 to get the number of payments. On the worked example that is 7.5% ÷ 12 = 0.625% a month (0.00625 as a decimal), and 5 × 12 = 60 payments. Skip the conversions and the payment comes out twelve times too big: the formula wants a monthly rate and a monthly count, never an annual rate and a yearly count.
Step 3 — Apply the amortizing-loan formula
Put the three numbers into the formula: M = $50,000.00 × 0.00625 × (1.00625)^60 ÷ ((1.00625)^60 − 1). The factor (1.00625)^60 works out to about 1.4533, so the payment is $50,000.00 × 0.00625 × 1.4533 ÷ 0.4533 = $1,001.90 a month. The formula is the standard amortizing-loan formula used by banks: each payment covers the month's interest first, and the rest pays down the loan, so the payment stays the same while the split between interest and principal shifts over the life of the loan.
Step 4 — Multiply for the total, subtract for the interest
Multiply the monthly payment by the number of payments for the total paid, then subtract the loan for the total interest. On the worked example the total paid is $1,001.90 × 60 = $60,114.00, and the total interest is $60,114.00 − $50,000.00 = $10,114.00. Round the payment to cents first, then multiply. At a 0% rate the payment is simply the loan divided by the number of payments: $50,000.00 ÷ 60 = $833.33, and 60 payments of $833.33 total $49,999.80 — twenty cents under the loan, because the payment is rounded to the cent.
Step 5 — Test a longer term and a lower rate
Run the same four steps with a longer term and with a lower rate, and watch the trade-off. Stretch the worked example to 10 years and the payment falls to $593.51 a month — but the interest more than doubles to $21,221.20. Cut the rate to 5% instead and the same loan costs $943.56 a month with $6,613.60 of interest; raise it to 10% and it costs $1,062.35 a month. Small rate differences move the payment by tens of dollars a month on a typical loan, and the term moves the total interest by thousands. The shortest term whose payment the business can actually make is usually the cheapest loan.
Step 6 — Check the payment against monthly cash flow
A payment is only affordable if the business brings in more than it pays out. Compare the $1,001.90 a month against what the business actually brings in each month, after rent, wages, stock and tax — not against what it hopes to bring in. A lender looks at the business's cash flow, not just the payment, and a payment that fits on paper but not in the bank account is how a good loan turns bad. If the payment is more than the monthly surplus, lengthen the term or borrow less — do not hope the revenue grows into it.
Step 7 — Check the result against the business loan calculator
Run the same numbers through the business loan calculator and check that it gives the same $1,001.90, $60,114.00 and $10,114.00 — if it does not, one of the three numbers is wrong, and that is the number to re-check. Then try the reverses: the smallest loan for a $1,000.00 payment is $49,905.06; the smallest rate for a $900.00 payment is 3.08%, which gives $900.21; and 8 years is the smallest whole term for a payment of $750.00 or less, at $694.19. The largest loan whose total interest stays at $10,000.00 or less is $49,438.44, at $9,999.96 of interest.
Three worked examples
A smaller loan. A $25,000.00 loan at 7.5% over 5 years costs $500.95 a month — $30,057.00 in total and $5,057.00 of interest. Halving the loan halves the payment almost exactly.
A bigger loan. A $100,000.00 loan at 7.5% over 5 years costs $2,003.79 a month — $120,227.40 in total and $20,227.40 of interest. Doubling the loan doubles the payment almost exactly.
A shorter term. A $50,000.00 loan at 7.5% over 3 years costs $1,555.31 a month — $55,991.16 in total and $5,991.16 of interest. The payment is $553.41 more a month than the 5-year loan, but the interest is $4,122.84 less.
The term-vs-interest trade-off
The term is the biggest lever on the total interest, and it works against the monthly payment. On the worked example, 3 years costs $1,555.31 a month and $5,991.16 of interest; 5 years costs $1,001.90 a month and $10,114.00 of interest; 10 years costs $593.51 a month and $21,221.20 of interest. Five extra years cut the payment by $408.39 a month but add $11,107.20 of interest — more than the payment you save. The payment falls fast at first and then flattens, so the first years off the term are the dearest. Pick the shortest term whose payment the business can actually make, and treat a longer term as a cost, not a saving.
What lenders actually look at
The payment is only one of the numbers a lender cares about. A lender also looks at the business's cash flow — whether the monthly surplus covers the payment with room to spare — at the business's credit history, at how long it has traded, and at what the money is for. A loan for equipment that earns its keep is a different risk from a loan that plugs a gap in the accounts. Fees, origination charges, variable rates and prepayment penalties are not in the formula, so the payment a lender quotes can differ by a few dollars from the one you calculate. Use the calculator to compare offers on equal footing — then read the quote, check the cash flow, and only then sign.