The payment formula
For a fixed-rate loan with equal monthly payments, the payment equals the loan amount times the monthly rate, divided by one minus the monthly rate raised to the negative number of payments. The monthly rate is the annual rate divided by twelve.
For a $50,000 loan at 7% over five years, the monthly rate is about 0.583% and there are 60 payments. The payment works out to about $990 a month. Over the five years you pay back roughly $59,400, so the interest is about $9,400.
Where each payment goes
Early payments are mostly interest, because the balance is at its highest. Each month the interest portion is the balance times the monthly rate, and the rest of the payment reduces principal. As the balance drops, interest shrinks and more of each payment goes to principal.
This is why paying extra early saves more than paying extra late. A dollar of principal removed early stops accruing interest for the rest of the loan.
The effect of extra payments
An extra $200 a month on the same loan pays it off in about 49 months instead of 60 and saves roughly $1,900 of interest. Check that your lender applies extra payments to principal and that there is no prepayment penalty.
If cash is tight, even an occasional extra payment helps. Keep an emergency buffer, since you cannot easily get paid-in principal back.
What the rate does not show
The stated rate is not the whole cost. Origination fees, closing costs, required insurance and a rate that changes with a benchmark can all raise what you pay. Ask the lender for the annual percentage rate and a full schedule of fees.
Compare offers on total cost over the term, not only the monthly payment. A lower payment from a longer term often means more interest overall.
Recording the loan
In your books, the loan is a liability. The payment is split: interest is an expense and principal reduces the loan balance. Booking the whole payment as an expense overstates costs and leaves the liability too high.
Ask the lender for an amortization schedule and tie your balance to their statement each month. A calculator gives a close estimate, but the lender's schedule is the one that governs.
Questions to ask the lender
Ask what the annual percentage rate is and whether it includes fees. Ask whether the rate is fixed or variable, how often payments are due, whether there is a prepayment penalty, and how late payments are handled.
Ask also whether the loan is secured by an asset, whether you personally guarantee it and what covenants apply, such as keeping a minimum balance or sharing financial statements. These terms affect risk as much as the payment does, so get them in writing.
Common questions
What if my loan rate is variable?
Payments can change when the rate changes. A fixed-rate calculator shows the payment at today's rate only.
Is a longer term better?
It lowers the monthly payment but usually raises total interest. Choose based on cash flow and total cost.
Can I pay a loan off early?
Often yes, but check for prepayment penalties in your loan agreement.
This guide is general information, not tax, legal or accounting advice. Rules, fees and due dates change; check with the IRS, the NJ Division of Taxation or a licensed professional for your situation.