30-Year Amortization Table: Monthly Payment Calculator

This calculator estimates the monthly principal-and-interest payment for a fixed-rate loan repaid over 30 years and shows total interest across the scheduled payments. Enter the loan amount and annual APR to see the payment and a year-by-year amortization table; it is for people checking how a long repayment schedule changes the balance over time.

Formula

For a fixed-rate loan with monthly payments, the unrounded payment is M = P × r / [1 − (1 + r)⁻ⁿ]. The calculator rounds the monthly payment to cents, as required for the displayed estimate. Here, P is the amount borrowed in dollars, r is the monthly interest rate as a decimal (APR ÷ 1,200), and n is the number of monthly payments (30 × 12 = 360). Total interest is the rounded monthly payment multiplied by 360, less the original principal.

The annual APR is entered as a percentage, so 6.5 means 6.5%, not 0.065. Dividing by 1,200 converts that percentage to a monthly decimal rate. For the example APR, r = 6.5 ÷ 1,200 = 0.0054166667. The formula assumes the same rate and payment amount throughout the schedule.

Worked Example

Using the calculator’s default loan amount of $200,000 and APR of 6.5%:

1. Monthly rate: r = 6.5 ÷ 1,200 = 0.0054166667.
2. Payment count: n = 30 × 12 = 360 months.
3. Substitute: M = 200,000 × 0.0054166667 ÷ [1 − (1.0054166667)⁻³⁶⁰].
4. Calculate and round to cents: monthly payment = $1,264.14.
5. Total of the 360 rounded payments: $1,264.14 × 360 = $455,090.40.
6. Estimated total interest: $455,090.40 − $200,000 = $255,090.40.

This is an arithmetic illustration, not a lender quote. A lender’s payment schedule may use different timing, rounding, or included charges.

Assumptions

• The interest rate is fixed for the full 30-year term.
• Payments are equal, made monthly, and begin one month after the loan starts.
• Interest compounds monthly at APR ÷ 12.
• The estimate includes principal and interest only; fees, taxes, insurance, PMI, and escrow are not included.

How a 30-Year Amortization Table Works

An amortization table breaks each scheduled payment into interest and principal, then shows the remaining balance. In the early months, interest is calculated on a relatively large outstanding balance, so more of the payment goes to interest. As principal falls, the interest portion typically shrinks and the principal portion grows. With a fixed rate and level payments, this pattern follows directly from the monthly balance.

To build a row, calculate that month’s interest as the opening balance multiplied by r. Subtract the interest from the monthly payment to get principal repaid, then subtract that principal from the opening balance. For example, on a $200,000 balance at the default monthly rate, the first month’s interest is about $1,083.33; the remainder of the $1,264.14 payment reduces principal. Values in a detailed table can differ by a cent because lenders round each period’s interest and may adjust the final payment.

The calculator summarizes the 360-month schedule with the payment and total interest rather than printing 360 rows. To make a year-by-year table, repeat the monthly balance calculation for 12 payments, record the ending balance, and continue for 30 years. The balance after k payments before any extra payments can also be calculated as P(1 + r)^k − M[(1 + r)^k − 1] ÷ r.

When to Use This Estimate

Use the result to understand the mechanics of a 30-year fixed-rate schedule or to compare arithmetic scenarios by entering different principal amounts or APRs supplied to you. The APR and loan amount are inputs, not market guidance; get the applicable figures and payment details from the lender. This page does not determine eligibility, approval, or an appropriate loan size.

Read the monthly payment as the modeled principal-and-interest amount, not necessarily the full amount due each month. Housing-related bills can include costs the formula does not model, and the lender’s disclosures explain the actual scheduled payment and any separate charges. Total interest assumes all 360 modeled payments are made as scheduled, without extra principal, skipped payments, fees, or a rate change.

Common Mistakes and Limits

• Entering APR as a decimal: enter 6.5 for 6.5%; the calculator converts it to a monthly rate.
• Confusing term and payment count: a 30-year term means 360 monthly payments, not 30 payments.
• Treating the estimate as the full bill: taxes, insurance, mortgage insurance, escrow, and fees are outside this formula.
• Ignoring rounding: the displayed monthly payment is rounded to cents, so multiplying it by 360 determines the displayed total interest. A lender’s period-by-period rounding can produce a small difference.
• Assuming every loan is fixed-rate: an adjustable rate, irregular payment timing, or a different compounding method does not fit these assumptions.

The model also does not account for extra payments, a payoff before 30 years, late charges, or changes to the contract. It is estimate arithmetic for education, never financial advice. The result is an estimate, and the lender’s disclosure gives the exact figures.

Frequently Asked Questions

What does a 30-year amortization table show?
It shows each scheduled payment’s interest and principal portions and the remaining balance over 360 monthly payments.

Does the calculator include property taxes or insurance?
No. It estimates principal and interest only; enter separate costs into your own budget using figures provided by the relevant biller or lender.

Why does the interest portion start larger?
Monthly interest is calculated on the outstanding balance, which is largest at the beginning of the schedule.

Does an extra payment change the table?
Yes. If applied to principal, an extra payment can alter the remaining balance and repayment schedule; this calculator assumes no extra payments.

Why might a lender’s number differ?
Rounding conventions, payment dates, fees, escrow items, and contract details can change the quoted payment or totals.

Final Thoughts

A 30-year amortization schedule helps explain how monthly payments gradually repay principal while covering interest. Use the calculator as a transparent estimate, then check the lender’s disclosure for the exact payment schedule and included costs.

Related

• What Is My Interest? Loan Interest Calculator
• K-1 Interest: What It Means for Taxable Income
• Valley First Credit Union Payment Calculator

in p | Loan amount | $ | 200000 | 1 | 100000000
in apr | Interest rate (APR) | % | 6.5 | 0.01 | 100
out pmt | Monthly payment | $ | round(p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(30 * 12)), 2) | 2
out int | Total interest | $ | pmt * 30 * 12 - p | 2