| Scenario | Loan | Rate | Frequency | IO term | Escrow | Extra principal | Start IO payment |
|---|---|---|---|---|---|---|---|
| Base | $250,000 | 6.25% | Monthly | 60 months | $300 | $0 | $1,602.08 |
| With extra principal | $250,000 | 6.25% | Monthly | 60 months | $300 | $100 | $1,702.08 |
The periodic interest-only payment (without extra principal) is:
Interest = Balance × (AnnualRate ÷ PeriodsPerYear).
If you add an optional principal amount during the interest-only phase:
Payment = Interest + ExtraPrincipal + Escrow + Fees, and the balance updates as:
NewBalance = OldBalance − ExtraPrincipal.
If you provide a total loan term, the post-IO payment is estimated using the standard amortization payment:
Pmt = (r × B) ÷ (1 − (1 + r)−n), where r is the periodic rate, B is balance, and n is remaining periods.
- Enter your loan amount and annual interest rate.
- Choose a payment frequency and set the interest-only term in months.
- Add escrow and fees per payment if they apply to your situation.
- Optionally add extra principal to see how faster paydown reduces interest.
- Enter a total loan term to estimate your payment after the interest-only period.
- Click Calculate, then export your results as CSV or PDF.
Interest-only payment basics
In an interest-only structure, each period pays interest on the current balance. For a $250,000 loan at 6.25% with monthly payments, the periodic rate is about 0.5208%. Interest-only interest starts near $1,302.08 monthly, before escrow or fees. Because principal is not required, cashflow is lower early, while the payoff balance stays high. Over 60 months, that interest alone totals about $78,124.80 if the balance stays unchanged.
Frequency and rate sensitivity
Payment frequency changes how often interest is computed and collected. Monthly uses 12 periods, biweekly uses 26, and weekly uses 52. A fixed annual rate is split across more periods, so the per‑period rate declines, but payments occur more often. Comparing schedules helps match payroll cycles and highlights how small rate changes ripple through every period. On a $250,000 balance, weekly interest per period is smaller, yet 52 payments per year can accelerate budgeting discipline for stable income households.
Escrow and recurring fees
Escrow adds predictable non‑interest costs such as taxes and insurance. If escrow is $300 monthly, the same example payment becomes about $1,602.08. Add a $25 servicing fee and the payment rises to roughly $1,627.08. Including these items prevents underestimating the amount you must actually budget for each due date.
Extra principal during interest-only
Adding extra principal converts a pure interest-only plan into a hybrid payoff. An extra $100 per month reduces the balance by $6,000 over 60 months. That reduction lowers later interest because interest equals balance times rate. The chart shows a downward balance slope and gradually shrinking interest bars, improving long‑term affordability.
Transition to amortization
After the interest-only period, the remaining balance must be repaid over the remaining term. Using the amortization payment formula, the post‑IO payment is typically higher than the initial IO payment. Modeling both phases clarifies payment shock risk and supports safer decisions on term length, refinance timing, and emergency reserves. Many lenders qualify borrowers using the higher amortizing payment, so planning with that figure reduces surprise more safely.
What is an interest-only payment?
An interest-only payment covers interest for the period, plus any escrow or fees you add. It does not reduce principal unless you choose an extra principal amount.
Why does my payment jump after the interest-only term?
When interest-only ends, the remaining balance must be repaid over fewer periods. The required amortizing payment is usually higher because it includes both interest and scheduled principal paydown.
Does payment frequency change total interest?
It can. More frequent payments may reduce interest slightly if principal is reduced earlier. If you pay strictly interest-only with no principal reduction, frequency mostly changes timing, not the underlying balance.
Should I include escrow and fees?
Yes, if you budget with “all-in” payments. Escrow for taxes and insurance and recurring fees can be a meaningful portion of your due amount, even though they are not interest.
How does extra principal help during interest-only?
Extra principal lowers the balance, which lowers future interest because interest is based on balance. Even small extra amounts can reduce the ending balance and soften the post-IO payment increase.
Is this result identical to my lender’s calculation?
Not always. Lenders may use different day-count rules, rounding, and fee structures. Use this tool for planning and comparison, then confirm terms in your loan documents.