Interest Only vs Amortizing Commercial Loan: Cash-Flow Trade-Offs
Interest-only payments cover interest without reducing principal by themselves. Amortizing payments include both interest and principal, reducing the balance over time. Comparing the structures requires the same principal, rate, and time horizon—not just a glance at which monthly payment is lower.
This guide compares two hypothetical five-year structures at $1 million principal and a fixed 6% nominal annual rate. One is interest only throughout those five years; the other uses 25-year amortization with a five-year term. Both use monthly, end-of-period payments and exclude fees, escrow, and voluntary principal payments.
A separate example then shows an IO period ending within a longer loan. These are educational models, not available financing terms, a product recommendation, or personalized financial advice. Actual repayment terms require document confirmation and qualified review.
In this guide: Repayment definitions · Monthly payments · Five-year balances · IO transition · Evaluation checklist
How do interest-only and amortizing repayments differ?
Interest-only payments do not reduce principal by themselves
In this simplified interest-only, or IO, structure, each regular payment equals interest on the outstanding balance for the month. With no principal payments, the balance remains $1 million.
That qualification matters. A voluntary principal payment would change the balance and subsequent interest calculation, but it is excluded from this comparison. The phrase “interest only” should not be interpreted as proof that principal can never change under any contract or payment history.
The lower regular outflow is a timing difference in repayment. It does not forgive principal or make it disappear at maturity.
Amortizing payments include principal and interest
An amortizing installment first covers the modeled interest for the period and applies the rest to principal. With a fixed payment and rate, declining principal reduces later interest, leaving more of each installment for principal.
To understand amortizing commercial loan payments, keep the repayment pace distinct from the maturity date. A loan can amortize every month yet still leave a balloon if its term ends before the amortization projection reaches zero.
Neither label alone tells you the rate structure, actual maturity, fees, or payment-reset rules. Those remain separate inputs to a complete comparison.
Compare monthly payments with identical principal and rate
Interest-only example at $1 million and 6%
The monthly rate is 0.06 ÷ 12 = 0.005. Monthly IO interest is therefore:
$1,000,000 × 0.005 = $5,000.00.
A full year of these unchanged payments totals $60,000.00. Every dollar in those scheduled payments is interest under this model; none reduces principal.
This calculation uses a simplified monthly convention, not actual-day interest accrual. A contractual schedule with different dates or accrual rules requires its own calculation.
The 25-year amortizing alternative
At the same principal and fixed nominal rate, 25-year amortization produces $6,443.01 monthly P&I. A full year totals $77,316.17 using unrounded payment precision.
[IMAGE: Interest-only versus amortizing commercial loan payments at $1 million and 6%: $5,000 versus $6,443.01 per month.]The monthly cash-outflow difference is approximately $1,443.01 at the start. In the amortizing case, that amount is the first payment’s principal component. Later principal components rise as the interest portion declines.
Calling the IO loan “cheaper” based on its payment would confuse lower current outflow with lower interest or total financing cost. To compare those measures, examine the same horizon and account for remaining principal separately.
Compare principal balances over the same five-year term
Interest-only leaves $1 million outstanding without principal payments
After 60 IO payments of $5,000, scheduled payments total $300,000.00. Principal remains $1,000,000.00 because none of those payments reduces it.
If this hypothetical loan matures at that five-year checkpoint, the remaining principal must still be addressed. The five-year interest total is not the total repayment obligation.
Amortization reduces the balance to about $899,320.87
After payment 60, the amortizing structure has reduced principal by $100,679.13, leaving $899,320.87. The balance is measured after the last regular installment, not before it.
| Measure | Five years interest only | Five-year term, 25-year amortization |
|---|---|---|
| Monthly scheduled payment | $5,000.00 | $6,443.01 |
| Annual scheduled payments | $60,000.00 | $77,316.17 |
| Total regular payments through month 60 | $300,000.00 | $386,580.84 |
| Interest through month 60 | $300,000.00 | $285,901.71 |
| Principal repaid through month 60 | $0.00 | $100,679.13 |
| Balance after payment 60 | $1,000,000.00 | $899,320.87 |
Both structures leave principal at the five-year maturity, but the amounts differ. The companion guide helps you assess the remaining balloon obligation without treating refinancing, a sale, or an extension as guaranteed.
Interest paid and total cash paid are different measures
The amortizing structure has higher regular cash payments but lower interest paid over these same 60 months. Part of its larger installments repays principal; that principal repayment is not an interest expense.
If the residual principal is also settled at month 60, total modeled cash paid over the full five-year horizon is $1,300,000.00 for IO and $1,285,901.71 for amortizing repayment. Those totals combine regular payments with the post-payment-60 residual and exclude fees or other contractual amounts.
This is a simple cash-sum comparison, not a present-value analysis or an all-in financing-cost assessment. It does not value the timing of retained cash. Its purpose is to prevent the lower IO installment from being mistaken for a smaller total principal obligation.
Calculations retain precision internally and round displayed amounts to cents. Contractual cent-rounding can cause small differences in actual payment and balance totals.
What happens when an interest-only period ends?
A reset into amortizing payments depends on the contract
The end of an IO period is not necessarily the loan’s maturity. A contract may define a later amortizing phase, but the rate, remaining repayment period, and payment timing must be verified. Do not assume the original amortization clock restarts automatically.
The first comparison above has five-year maturity. It does not assume the loan continues into a sixth year. The following example is a separate structure used only to illustrate a payment transition.
A separate 25-year loan illustration with five years IO and 20 years left
Assume a hypothetical 25-year loan with five years of IO payments followed by 20 years of amortizing payments. Assume the 6% nominal rate stays fixed throughout and no principal is voluntarily repaid during IO.
At the transition, principal is still $1 million. Amortizing it across the remaining 240 months produces $7,164.31 monthly P&I, compared with $5,000 during IO. The payment increase is approximately $2,164.31 per month.
This is not the $6,443.01 payment from the 300-month amortization scenario. Fewer remaining repayment periods require a different installment at the same balance and rate.
For a full year after this hypothetical transition, scheduled P&I is $85,971.73. With illustrative annual NOI of $100,000, the simplified coverage ratio is about 1.16×, compared with 1.67× during a full IO year. These ratios are arithmetic examples, not approval thresholds.
Use matched periods to test debt-service coverage after an IO period. If a reporting year includes both phases, sum the actual payments in each phase rather than annualizing only one payment amount.
How to evaluate cash flow, maturity exposure, and repayment terms
Near-term liquidity versus principal reduction
IO preserves more cash from the scheduled-payment perspective in this matched example. Amortization reduces outstanding principal sooner. Those outcomes can be measured without declaring either structure universally superior.
The comparison should show what happens to any retained cash rather than assuming it remains available at maturity. Cash not used for principal today and principal still owed later are separate entries, not an automatic offset.
Coverage at the payment reset and funding at maturity
Analyze a payment reset and a maturity balance separately. The reset affects recurring outflow; maturity creates a principal funding checkpoint. A model can show adequate current IO coverage while leaving either issue unresolved.
Refinancing, a sale, or an extension remains a conditional event. Neither positive modeled coverage nor a lower current installment guarantees that event will occur on time or provide sufficient funds.
Verify IO length, subsequent amortization, rate changes, and maturity
An educational comparison checklist includes:
- Exact IO start and end dates.
- Principal expected at the transition.
- Subsequent amortization periods and payment timing.
- Fixed-rate duration or documented reset provisions.
- Contractual maturity and final installment timing.
- Applicable fees, costs, and prepayment conditions for review.
- Whether balances are shown before or after the final payment.
Use the actual documents for these inputs. A label such as “five years IO” does not establish the later repayment period or extension rights by itself.
Compare realistic cash flows rather than payment alone
Keep monthly outflow, interest paid, principal reduction, and residual balance in separate columns. Add verified costs separately; do not invent pricing premiums or lender eligibility rules to make one option look better.
A useful next step is to build matched scenarios and identify which assumptions still need confirmation. That produces a clearer discussion with a lender or adviser than selecting a structure solely because its first payment is smaller.
FAQ
Does interest only mean principal is forgiven?
No. Interest payments alone leave principal unchanged. In the five-year IO example, $1 million remains after payment 60.
Can an amortizing loan still have a balloon?
Yes. The five-year-term, 25-year-amortization example leaves $899,320.87 after the final regular term installment.
Why is the payment after IO $7,164.31 rather than $6,443.01?
The separate transition example repays $1 million across 240 remaining months, not 300, at the same assumed 6% rate.
Is the lower monthly payment the lower-cost loan?
Not necessarily. In this matched example, IO has lower regular outflow but more interest over five years. A complete cost comparison would also need verified fees and other relevant assumptions.