# Amortization schedule calculator

> Amortization calculator: payment, dated schedule and yearly totals for monthly, biweekly or weekly payments, with principal and interest in each.

Interactive version: https://www.calcopenly.com/finance/amortization-schedule-calculator
Subject: Finance calculators

An amortization schedule splits every loan payment into interest and principal. Each period's interest is the balance times the rate per period, and the rest of the fixed payment reduces the balance, so the interest share falls with every payment. The payment is L × i × (1 + i)^n ÷ ((1 + i)^n − 1), where L is the loan, i the rate per period and n the number of payments.

With the defaults, 250,000 at 6.5% for 30 years, the payment is 1,580.17 a month and interest totals 318,861.22. The first payment is 1,354.17 of interest and only 226.00 of principal; principal overtakes interest at payment 233. Paying half the monthly amount every two weeks (accelerated biweekly) ends the loan after 628 payments, about 24.2 years, and saves 73,434.82 of interest.

The rate is fixed and every payment is the same, apart from a last payment that clears the remaining cents. Biweekly and weekly rates are the annual rate ÷ 26 or ÷ 52 unless you choose another compounding under More options.

## Inputs

- **Loan amount**
- **Interest rate (per year)**
- **Loan term**
- **Term in** (options: Years, Months)
- **Payment frequency** (options: Monthly, Biweekly, Weekly, Accelerated biweekly, Accelerated weekly)
- **First payment date**
- **Table shows** (options: Every payment, Yearly totals)
- **Interest compounds**: Most US loans charge the annual rate ÷ payments per year. A Canadian mortgage must state its rate calculated yearly or half-yearly, not in advance (Interest Act, section 6). (options: With each payment, Monthly, Twice a year (Canada), Once a year)
- **Extra with every payment**

## Results

- Payment — main result
- Number of payments
- Total interest
- Total of all payments
- Last payment
- Interest saved compared with monthly payments
- Rate per payment period
- Effective annual rate

## Formula

$$
A = \frac{L\,i\,(1+i)^n}{(1+i)^n - 1},\qquad i = \begin{cases} j/p & \text{compounding with each payment} \\ (1 + j/m)^{m/p} - 1 & \text{compounding } m \text{ times a year} \end{cases}
$$

## Worked examples

### 200,000 at 6% for 15 years

- Loan amount: 200,000
- Interest rate (per year): 6%
- Loan term: 15
- Term in: Years
- Payment frequency: Monthly
- First payment date: 2026-01-01
- Table shows: Every payment
- Interest compounds: With each payment
- Extra with every payment: 0
- **Payment: 1,687.71 per month**
- **Number of payments: 180**
- **Total interest: 103,788.46**
- **Total of all payments: 303,788.46**
- **Last payment: 2040-12-01**
- Checked against: Calculator.net amortization calculator, published default output: 1,687.71 a month, 103,788.46 total interest

### 10,000 at 8% over 10 months

- Loan amount: 10,000
- Interest rate (per year): 8%
- Loan term: 10
- Term in: Months
- Payment frequency: Monthly
- First payment date: in 1 month
- Table shows: Every payment
- Interest compounds: With each payment
- Extra with every payment: 0
- **Payment: 1,037.03 per month**
- **Number of payments: 10**
- Checked against: Microsoft PMT function documentation: =PMT(8%/12, 10, 10000) returns ($1,037.03)

### Biweekly payments sized to a 15-year term

- Loan amount: 200,000
- Interest rate (per year): 6%
- Loan term: 15
- Term in: Years
- Payment frequency: Biweekly
- First payment date: 2026-01-01
- Table shows: Every payment
- Interest compounds: With each payment
- Extra with every payment: 0
- **Payment: 778.30 every 2 weeks**
- **Number of payments: 390**
- **Total interest: 103,536.93**
- **Interest saved compared with monthly payments: 251.53**
- **Last payment: 2040-11-29**
- Checked against: Python decimal: annuity at 6%/26 over 390 periods; last payment 389 × 14 days after 2026-01-01

### Canadian mortgage: 5% compounded half-yearly

- Loan amount: 300,000
- Interest rate (per year): 5%
- Loan term: 25
- Term in: Years
- Payment frequency: Monthly
- First payment date: in 1 month
- Table shows: Every payment
- Interest compounds: Twice a year (Canada)
- Extra with every payment: 0
- **Payment: 1,744.81 per month**
- **Effective annual rate: 5.0625%**
- **Total interest: 223,444.49**
- **Rate per payment period: 0.412392%**
- Checked against: Python decimal: monthly rate (1.025)^(1/6) − 1, annuity over 300 months; effective rate 1.025² − 1

### Accelerated biweekly on 300,000 at 6.5% for 30 years

- Loan amount: 300,000
- Interest rate (per year): 6.5%
- Loan term: 30
- Term in: Years
- Payment frequency: Accelerated biweekly
- First payment date: 2026-01-01
- Table shows: Every payment
- Interest compounds: With each payment
- Extra with every payment: 0
- **Payment: 948.10 every 2 weeks**
- **Number of payments: 628**
- **Total interest: 294,511.68**
- **Interest saved compared with monthly payments: 88,121.78**
- **Last payment: 2050-01-13**
- Checked against: Python decimal loop: half of the 1,896.20 monthly payment every 14 days at 6.5%/26 until the balance is zero

### Zero-rate loan paid weekly

- Loan amount: 5200
- Interest rate (per year): 0%
- Loan term: 1
- Term in: Years
- Payment frequency: Weekly
- First payment date: in 1 month
- Table shows: Every payment
- Interest compounds: With each payment
- Extra with every payment: 0
- **Payment: 100.00 per week**
- **Number of payments: 52**
- **Total interest: 0.00**
- **Effective annual rate: 0.0000%**
- Checked against: 5,200 ÷ 52 by definition at a zero rate

## Questions

### How do you calculate an amortization schedule?

Work out the fixed payment, then repeat three steps for every period: interest = balance × periodic rate, principal = payment − interest, new balance = balance − principal. For 250,000 at 6.5% over 30 years the payment is 1,580.17; month 1 interest is 250,000 × 6.5% ÷ 12 = 1,354.17, principal is 226.00 and the balance falls to 249,774.00. Excel's PMT, IPMT and PPMT functions give the same figures.

### Why does most of an early mortgage payment go to interest?

Interest is charged on the balance still owed, and the balance is largest at the start. On 250,000 at 6.5% over 30 years, 1,354.17 of the first 1,580.17 payment is interest. The principal part grows each month and first exceeds the interest part at payment 233, in year 20. Extra payments move that point earlier because they cut the balance directly.

### Do biweekly payments save interest?

Only the accelerated kind saves much. A biweekly payment sized to finish on the original 30-year term, 728.97 on 250,000 at 6.5%, saves 268.06 against monthly payments. Paying half the monthly payment, 790.09, every two weeks makes 26 half-payments, the same as 13 monthly payments a year; that ends the loan after about 24.2 years and saves 73,434.82.

### How much interest does a 15-year loan save over a 30-year loan?

Borrowing 250,000 at 6.5%, a 30-year loan costs 1,580.17 a month and 318,861.22 of interest; over 15 years the payment rises to 2,177.77 and interest falls to 141,998.31, a saving of 176,862.91 at the same rate. Fifteen-year rates are lower in practice: Freddie Mac's survey of September 24, 2026, averaged 6.42% for 15-year and 7.03% for 30-year fixed loans.

### How are Canadian mortgage payments calculated?

Canada's Interest Act (section 6) requires a mortgage to state its rate calculated yearly or half-yearly, not in advance, so the monthly rate is the equivalent of the half-yearly rate: (1 + 5% ÷ 2)^(1/6) − 1 = 0.41239% for a 5% mortgage. On 300,000 over 25 years that gives 1,744.81 a month, against 1,753.77 if the 5% compounded monthly. Choose "Twice a year (Canada)" under More options.

### How accurate is the amortization schedule calculator?

Accuracy depends on your inputs and the method's assumptions. Decimal arithmetic uses 50 significant digits, but estimates, numerical methods and source data can be less precise; the displayed rounding does not remove those limits. It is checked against 6 worked examples whose answers come from independent sources; for example, “200,000 at 6% for 15 years” is checked against Calculator.net amortization calculator, published default output: 1,687.71 a month, 103,788.46 total interest.

### Where does the method come from?

Microsoft Excel PMT function (payment for a loan); Interest Act (Canada), R.S.C. 1985, c. I-15, section 6 — mortgage interest compounded half-yearly or yearly; Freddie Mac Primary Mortgage Market Survey (weekly 30-year and 15-year fixed rates); Consumer Financial Protection Bureau — How does paying down a mortgage work?.

## Sources

- [Microsoft Excel PMT function (payment for a loan)](https://support.microsoft.com/office/pmt-function-0214da64-9a63-4996-bc20-214433fa6441)
- [Interest Act (Canada), R.S.C. 1985, c. I-15, section 6 — mortgage interest compounded half-yearly or yearly](https://laws-lois.justice.gc.ca/eng/acts/i-15/page-1.html)
- [Freddie Mac Primary Mortgage Market Survey (weekly 30-year and 15-year fixed rates)](https://www.freddiemac.com/pmms)
- [Consumer Financial Protection Bureau — How does paying down a mortgage work?](https://www.consumerfinance.gov/ask-cfpb/what-is-amortization-and-how-could-it-affect-my-loan-en-1943/)

_Note: financial information, not professional advice._