How to book loan payments: principal and interest

To book loan payments as principal and interest, split every payment according to the loan's amortization schedule: the interest portion goes to Interest Expense, the principal portion reduces the loan liability, and at month end the liability balance is tied to the lender's statement. Done that way, the balance sheet shows what the business actually owes, the P&L shows the true cost of borrowing, and the year-end interest figure is already right.

We run an accounting firm, and misbooked loans are the single most common balance sheet error we find when we take over a file. The fix is not complicated. It just has to be done every month, by rule, rather than once a year by the tax preparer.

Why doesn't my loan balance match the bank's statement?

Two mistakes account for almost every wrong loan balance, and they're mirror images.

All to the loan. The bookkeeper sees a $1,850 debit to the lender and codes the whole thing against the loan liability. The balance drops by $1,850 a month, faster than reality, and after three years the books show a $22,000 loan that the lender says is $41,000. Interest expense on the P&L is zero, profit is overstated, and the tax return either picked it up from the lender's year-end letter (so the return and the books disagree) or missed the deduction entirely.

All to interest. The opposite. Every payment coded to Interest Expense or, worse, to a catch-all like Bank Charges. The loan balance on the books never moves from the original amount. The P&L carries $22,200 of "interest" that's mostly principal, profit is understated, and the balance sheet shows debt the business paid off years ago. We've seen vehicle loans that were fully paid still sitting at their original balance three years after the title arrived.

A third, subtler version: the split is done, but from the wrong schedule. The bookkeeper used the original amortization and the client made an extra principal payment in year two, or the loan has a variable rate, or there was a deferral in 2020 that pushed everything. The split is close, the balance drifts a little each month, and nobody notices until a refinance.

All three have the same symptom: the balance in the books and the balance on the lender's statement disagree, and nobody looks at the lender's statement because the payment is "handled."

What is a loan amortization schedule for bookkeeping?

The amortization schedule is the list of every scheduled payment with its interest and principal portions and the balance after each. It's built from four facts on the note: original principal, annual interest rate, term (number of payments), and first payment date. From those, each month's interest is the prior balance times the monthly rate, the principal is the payment minus that interest, and the new balance is the old balance minus the principal.

On a $50,000 note at 8 percent over 60 months, the payment is about $1,014. The first month's interest is $50,000 times 8 percent divided by 12, or $333, so principal is $681 and the balance drops to $49,319. By month 30 the interest portion is roughly $200 and the principal is $814. By month 59 it's almost all principal. That drift is why a fixed split ("code 30 percent to interest") is wrong every month except one.

Get the four facts from the note itself, not from the client's memory. If the client can't find the note, the lender's first statement usually has the original balance, rate, and payment, and the first month's interest on the statement lets you back into the rate. Build the schedule once, store it against the loan, and every payment for the life of the note is already split before it arrives.

For notes with a variable rate, a balloon, interest-only periods, or an SBA loan with a fee and a guarantee, the schedule needs those terms, and the monthly tie-out becomes more important, not less, because the schedule will need updating when the rate resets.

Splitting payments from the bank feed by rule

Once the schedule exists, the monthly work is mechanical. The lender's debit arrives in the bank feed. A rule recognizes the payee and the amount, looks up the current row in the schedule, and posts a split: interest to Interest Expense, principal to the loan liability. The bookkeeper reviews it, doesn't type it.

A few rules for the rule:

• Match on the payee and the loan, not just the amount. A client with two vehicle loans at the same lender needs two rules, and the amounts are the only way to tell them apart until the payments are set up on separate schedules.
• Escrow and fees are their own lines. A mortgage payment that includes property tax and insurance escrow splits three ways: interest, principal, and escrow (an asset, not an expense, until the lender pays the tax bill). A loan with a monthly servicing fee splits interest, principal, and Bank Fees.
• Extra principal is an exception, not a rule. When the client pays more than the scheduled amount, the excess is principal and the schedule has to be rebuilt from that date. Flag it; don't let the rule swallow it.
• Missed and late payments shift the schedule too. A month skipped means the next month's interest is higher because the balance didn't drop.

Monthly tie-out to the lender statement

The rule gets you close. The lender's statement makes you right. Once a month, for every loan, compare the book balance after the last payment to the balance on the lender's statement for the same date. The difference should be zero, or a few dollars of daily-interest timing that you understand.

When it isn't, the causes are the ones above: a missed extra payment, a rate change, a fee you didn't split, or a payment that came out of a different bank account and never hit the feed at all. Fix the schedule, post the catch-up, and move on. Ten minutes a loan.

The year-end payoff for that discipline is that the lender's interest letter (Form 1098 for a mortgage, a plain statement for most commercial and vehicle loans) matches the Interest Expense account to the dollar. The tax preparer doesn't have to choose between the books and the letter, and the balance sheet on the return matches the one the bank sees when the client applies for the next loan. Lenders read the balance sheet. A business that shows $22,000 of debt when the lender's own system says $41,000 has a credibility problem before the application is read.

Vehicle loans, lines of credit, and owner-financed notes

Vehicle loans are the easiest and the most often wrong, because they're small and the payment feels like an expense. Book the vehicle as a fixed asset at full cost, the loan as a liability, and the down payment from cash, all on the purchase date. Then amortize. A truck bought in March with a $45,000 note is not $9,000 of "auto expense" by December.

Lines of credit don't amortize. Interest is charged on the drawn balance and billed monthly; principal moves whenever the client draws or repays. Book the interest from the statement each month, book draws and repayments as transfers between the bank and the LOC liability, and tie the balance to the statement. The mistake here is coding a draw as revenue or a repayment as expense.

Owner-financed and seller notes have no statement, which is why they drift the most. Build the schedule from the note, post the split every month whether or not anyone sends a reminder, and treat the borrower's and lender's books as the two sides of one tie-out. If the note is between related entities, that's the same discipline as any intercompany balance: both sides, every month, zero difference. For landlords carrying seller financing on a property, the same per-property balance sheet that holds the mortgage should hold the note, which we cover in real double-entry books for landlords.

Where the platform comes in

Disclosure: Woven is our product. Its loan sub-ledger builds the amortization schedule from the note, splits each lender payment from the bank feed by rule into interest, principal, and escrow or fees, and ties the running balance to the lender statement each month, and the asset acquisition flow books the asset, the loan, and the down payment from the purchase documents in one entry. To see a loan tied to its lender on live books, book a demo.