One mortgage payment leaves your account each month, and it looks like one number. For a rental, it is really three different things wearing a single coat: deductible interest, non-deductible principal, and an escrow transfer that is neither. If your books record the whole payment as a single “mortgage” expense, your Schedule E is wrong in three directions at once, and the error compounds every month.
The fix is not complicated, but it is unforgiving about details. You need to know which piece is a deduction, which piece is not, and the exact year each one counts. Get those three rules straight and the tracking is a monthly habit of a few minutes. Here is the breakdown, piece by piece, with a worked payment so the math is concrete.
The three pieces of one payment
Say you buy a duplex for $340,000 and finance $270,000 at 7% on a 30-year note. The principal and interest portion of that loan is about $1,796 a month. Your servicer also collects escrow for property taxes and landlord insurance, say $520 a month combined. So the payment that clears your bank is roughly $2,316. That single debit is three separate things:
- Interest: in the first month, about $1,575 of that $1,796 is interest. This is the rent you pay the bank for the money, and it is a deductible rental expense.
- Principal: the other $221 pays down the loan balance. You are buying a slice of the building back from the lender. That is not an expense, so it is not deductible.
- Escrow: the $520 goes into a holding account the servicer controls. It is your money parked until a bill comes due. Putting money in is not a deduction. The deduction happens later, when the servicer pays the bill.
The interest and principal split is not fixed. Early in a 30-year loan almost the whole payment is interest, and the principal share creeps up every month as the balance falls. By year 15 the two are roughly even. That is why a flat “75% interest” estimate drifts wrong over time. The only honest source for the monthly split is the loan's amortization schedule, which your lender can provide or you can compute from the rate, balance, and term.
Principal is never the deduction
This is the single most common mistake I see in a self-managed spreadsheet, and it is expensive in both directions. People either deduct the whole payment, which overstates the loss and invites an adjustment, or they get nervous and deduct nothing, which throws away a real interest deduction. Both come from treating the payment as one thing.
The logic is worth holding onto: a deduction is money you spent that left your wealth. Interest left your wealth, it went to the bank for nothing you keep. Principal did not leave your wealth, it converted cash into equity in the building. You still have it, it only changed shape. You already capture the building's cost through depreciation, so deducting principal too would be claiming the same dollars twice.
Principal paydown does help you, it helps on the balance sheet, not the tax return. Every dollar of principal is a dollar of equity you now own. If you track your portfolio's value and debt over time, that is where principal shows up, growing your equity quietly while the interest line shrinks.
Escrow: deduct what the lender paid out, not what you paid in
Escrow is where timing trips people. You fund escrow monthly, but the servicer pays the tax and insurance bills on their own schedule, often one or two large disbursements a year. The deduction follows the disbursement, not your monthly deposit.
Continue the duplex example. You paid $520 a month into escrow, $6,240 for the year. But suppose the servicer disbursed $4,800 in property taxes and $1,300 in insurance, $6,100 total, and the remaining $140 sat in the cushion. Your deductions for the year are the $4,800 on line 16 (taxes) and the $1,300 on line 9 (insurance). The $6,240 you deposited is not a number that appears anywhere on Schedule E, and the $140 still sitting in escrow is not deductible until it is spent. This is the escrow-disbursement rule, and it is spelled out in IRS Publication 527: you deduct real estate taxes in the year the taxing authority is actually paid.
Form 1098 only tells part of the story
In January your lender sends a Form 1098, the Mortgage Interest Statement. Box 1 shows the interest you paid for the year, which is your starting point for line 12. That number is reliable and it is the one piece of this puzzle the lender hands you clean.
What Form 1098 does not give you is the rest. It does not break out principal, because principal is not a tax item. Box 10 may show real estate taxes the servicer disbursed, but lenders are inconsistent about filling it in, and when it is blank you have to get the disbursed tax from your annual escrow analysis statement instead. So the 1098 settles line 12 and nothing else. For taxes and insurance you go to the escrow statement; for principal you go to the amortization schedule. Three documents, three lines.
How this lands on Schedule E line 12
When all three pieces are tracked, the form is short. The deductible interest from Box 1 goes on Schedule E line 12, “Mortgage interest paid to banks.” The disbursed property tax goes on line 16, the disbursed insurance on line 9. Principal appears nowhere. Escrow deposits appear nowhere. The Schedule E instructions are explicit that line 12 is interest paid to financial institutions, not your whole payment.
The reason this is worth setting up correctly once is that it never gets easier by deferring it. If you wait until March to untangle twelve payments, you are reverse-engineering an amortization schedule from bank debits and chasing an escrow statement you filed somewhere. If instead each payment is split the day it clears, the year-end work is reading three numbers off three statements and confirming they match what you recorded. The financing math matters too: before you take on a loan, the way it splits into interest and principal feeds straight into your refinance decisions and your cash-on-cash return, which is the difference between a property that funds your growing portfolio and one that quietly bleeds it.
Tracking it without a forensic project
You can do the whole split in a spreadsheet if you are disciplined: one column for interest, one for principal, one for escrow, and a separate tab where you record the actual tax and insurance disbursements when they happen. The discipline is the catch. The interest and principal numbers change every single month, so a static formula goes stale, and the escrow timing means your monthly deposit and your deductible disbursement live in different rows entirely. That gap is exactly where spreadsheets drop a number.
This is the part of the books I built rents.ai to handle: you enter the loan once, and it splits every recurring mortgage payment into deductible interest, non-deductible principal, and escrow, keeping principal and escrow out of NOI and Schedule E where they do not belong. It will not pull the numbers from your bank for you, you record the payment, but once recorded the three-way split and the line 12 figure are a lookup instead of a reconstruction. The disbursement timing on taxes still needs you to log when the servicer actually pays, because no software can know the date a bill cleared unless you tell it.
These are estimates to organize your year for your CPA, not tax advice. The interest, principal, and escrow rules have edge cases this guide skips, points and prepaid interest and mixed-use loans among them. Bring your accountant clean records, the 1098, the escrow statement, and the amortization schedule, and let them make the calls.