What this tool does
The Loan Payment Table Generator builds a grid of fixed monthly payments for a fully-amortizing loan. Instead of computing one payment at a time, it varies two quantities across the rows and columns of a table while holding a third constant, so you can compare many loan-amount and term scenarios at a glance. It works for any installment loan with end-of-period payments, such as a car loan, personal loan or mortgage. Amounts are treated as plain US dollars and the rate as an annual percentage.
How to use it
Pick an axis layout: "Months and Loan" (default) holds the annual rate constant and varies loan amount down the rows and term across the columns; "Rate and Loan" holds the term constant; "Rate and Months" holds the loan amount constant. Enter the constant rate, the starting value and increment for each axis, and how many rows and columns to generate. The first column starts at "Starting Month" and adds "Increments (months)" each step; the first row starts at "Starting Amount" and adds "Increments ($)" each step.
The formula explained
Each cell uses the standard amortization formula $$\text{PMT} = PV \times r \times \dfrac{(1+r)^n}{(1+r)^n - 1}$$ where \(r\) is the monthly rate equal to the annual percent divided by 100 and then by 12, and \(n\) is the number of monthly payments. If the rate is zero the formula would divide by zero, so the tool falls back to $$\text{PMT} = \dfrac{PV}{n}$$
Worked example
Take a $15,000 loan at 3.125% annual rate over 24 months. The monthly rate is \(3.125 / 100 / 12 = 0.00260417\). Then \((1+r)^{24} = 1.064466\), so $$\text{PMT} = 15000 \times 0.00260417 \times \frac{1.064466}{0.064466} = \$645.55$$ per month, the top-left cell of the default table.
FAQ
Does this include taxes, fees or insurance? No. It computes the pure principal-and-interest payment only.
What if I set the rate to 0%? The payment becomes the loan amount divided by the number of months (a straight-line repayment).
How is total interest found? Multiply any cell's payment by its number of months and subtract the loan amount: \(\text{total interest} = \text{PMT} \times n - PV\).
