Inputs
₨
Enter principal. Currency is display-only and does not affect math.
%
years
₨
Key Results
Periodic Payment: —
Annual Debt Service: —
Loan Constant (periodic): —
Loan Constant (annual): —
Term periods: — | Periodic rate: —
Amortization Chart
Balance line and stacked bars for interest and principal by period.
Amortization Schedule
| Period | Payment | Interest | Principal | Extra | Balance |
|---|
Rows limited to 1200 periods for performance.
Example Loan Constants
Quick reference for typical combinations. Constants shown as annual and periodic ratios (ADS/Loan and Payment/Loan).
| Loan | Rate | Years | Py | Payment | Const Annual | Const Periodic |
|---|
Formula Used
The loan constant is the ratio of periodic (or annual) debt service to the original loan amount. For a fully-amortizing loan with nominal annual rate \( R \), payments per year \( m \), term in years \( Y \), loan \( P \), the periodic rate is \( i = R/m \) and number of periods is \( N = mY \).
- Periodic payment: \( A = P \cdot \dfrac{i}{1 - (1+i)^{-N}} \) for \( i > 0 \).
- Zero-rate edge case: if \( i = 0 \), then \( A = P/N \).
- Periodic constant: \( C_p = \dfrac{A}{P} \).
- Annual constant: \( C_a = m \cdot C_p = \dfrac{mA}{P} = \dfrac{\text{ADS}}{P} \).
With extra payments, amortization finishes sooner; constants are still computed from the scheduled payment so they remain comparable across loans.
How to Use
- Enter loan amount, annual rate, term, and choose payments per year.
- Optionally add an extra amount each period to accelerate payoff.
- Press Calculate to compute payment, debt service, and constants.
- Explore the chart and scroll the schedule; export CSV or PDF anytime.
- Compare scenarios by altering rate, term, or frequency and noting constants.
FAQs
The interest rate is the cost of borrowing per year, while the loan constant reflects the total annual debt service (principal plus interest) as a fraction of the original loan. Two loans with the same rate but different terms will have different constants.
More frequent payments (higher \( m \)) usually lower interest carry, slightly reducing total interest and adjusting the annual constant because ADS equals \( m \) times the periodic payment.
The conventional constant is derived from the scheduled payment. Extra payments accelerate payoff and cut interest but the constant is typically kept for apples-to-apples comparisons across loans.
If \( i = 0 \), the payment is \( P/N \). All payment goes to principal; interest is always zero. The annual constant becomes \( m/N = 1/Y \).
Yes. The annual constant equals ADS/Loan. Given a target DSCR and NOI you can estimate supportable loan \( \approx \frac{\text{NOI}}{\text{DSCR} \cdot C_a} \). This calculator provides \( C_a \) precisely.