How to calculate mortgage interest rates: 3 tips for calculating installment payments.

When considering buying a house or property, most people's first concern is how mortgage interest rates are calculated and the monthly payments. Without a clear understanding of the calculation, it's easy to choose a loan with high interest rates, leading to long repayment periods. This article will help you understand how to calculate mortgage interest rates simply and practically, allowing you to compare different bank loan packages and make a decision that suits your financial capabilities. In just a few minutes of reading, you'll understand how much you're borrowing, how much you're paying each month, and why those numbers are important.

Tip 1: How to quickly calculate your mortgage payments using Excel

Step 1: Understand the PMT function when calculating mortgage interest rates using Excel.

What is the PMT function and what is it used for?
The PMT function is a function used to calculate the periodic payment for a loan, commonly used to determine the monthly payment amount when taking out a mortgage .

• This function is available in most popular spreadsheet software such as:

  • Microsoft Excel

  • Google Sheets

  • Apple Numbers

• PMT automatically calculates the loan amount based on the basic loan information:

  • Mortgage interest rates

  • Loan term (number of repayment installments)

  • Initial loan amount (principal)

Why should you use the PMT function to calculate mortgage interest rates?
Using the PMT function helps you avoid confusion when calculating manually and makes it easy to compare different loan options.

• Know exactly how much you have to pay each month.

• Proactively manage your personal cash flow.

• It's easy to compare mortgage loan packages between banks.

• Suitable for both first-time and experienced borrowers.

The simplest approach with the PMT function
For ease of understanding and practice, you can start with Microsoft Excel – the most widely used software today.

• Entering functions and parameters in Excel is very intuitive.

• The PMT function structure is almost identical across Google Sheets and Apple Numbers.

• If you're using other software, simply check the help section or user manual for similar instructions.

Step 2: How to use the PMT function to calculate your monthly mortgage payment.

1. Enter the PMT function in the spreadsheet.
Start by typing the following formula into any cell in the spreadsheet:

• =PMT(

Immediately afterwards, the software will suggest the function structure:

• PMT(rate, nper, pv, [fv], [type])

In there:

• The first 3 parameters are mandatory.

• The last two parameters are optional and can be left blank.

2. Determine the monthly loan interest rate.
rate refers to the monthly mortgage interest rate , not the annual interest rate stated in the contract.

Calculation method:

• Divide the annual interest rate by 12.

• Then convert it to decimal form.

Here's a specific example:

• Annual interest rate: 6%

• 6% ÷ 12 = 0.5%

• 0.5% ÷ 100 = 0.005

→ The rate value to enter is 0.005

You can also calculate it in another way:

• 6% ÷ 100 = 0.06

• 0.06 ÷ 12 = 0.005

The results are the same and both are correct when calculating monthly mortgage interest .

3. Determine nper – the total number of repayment periods.
nper is the total number of payments you have to make throughout the loan term.

Calculation method:

• Loan term × 12 (if paying monthly)

For example:

• Loan term: 15 years

• 15 × 12 = 180

→ The value of nper is 180

4. Determine the PV – the initial loan amount.
pv is the principal amount you borrow , excluding interest.

For example:

• Loan amount: USD 100,000 (or equivalent to VND)

• The pv value is 100,000.

Note: Typically, when entering data into Excel, pv will use negative numbers so that the resulting payment is a positive number, making it easier to track.

5. Ignore fv and type if not necessary.

• fv (future value) and type (repayment date) can be left blank.

• The software will automatically assume the default value is 0, which is suitable for most monthly installment mortgage loans.

Step 3: Enter the formula and see the monthly payment amount.

How to enter the complete PMT formula
You enter the calculated values ​​from the previous steps into the function one by one:

• Monthly interest rate

• Total number of installments ( nper )

• Initial loan amount ( pv )

Here's a specific example:

• Monthly interest rate: 0.005

• Number of installments: 180

• Loan amount: 100,000

The formula will be:

• =PMT(0.005, 180, 100000)

Understanding the displayed results correctly
After pressing Enter, Excel or Google Sheets will display the monthly payment amount.

• The result is usually a negative number.

• This is perfectly normal.

• The software uses negative numbers to represent monthly expenses , not income.

Why is this step important when calculating mortgage interest rates?

• It helps you know exactly how much you have to pay each month.

• It's easy to compare different loan options simply by changing the interest rate or loan term.

• Proactively assess your financial capabilities before signing a mortgage loan agreement.

Step 4: Analyze the results returned from the PMT function.

What do the results from the PMT function mean?
The number returned by the PMT function is the total amount you have to pay each month , including both principal and interest.

• This is the monthly payment amount for the mortgage loan.

• This figure accurately reflects your actual financial obligations.

Why is the result a negative number?
If you see a negative number as the result, don't worry.

• This is not a formula entry error.

• Default spreadsheet software:

  • Amount received: positive number

  • Amounts spent (debt repayment): negative number

• Since debt repayment is an expense, PMT shows a negative value.

How to read the results more easily
To make it easier to track and compare loan options, you can:

• Multiply the result by -1 to convert it to a positive number.

• Or simply understand that the absolute value is the amount of money you have to pay each month.

Specific examples
With the formula entered earlier:

• =PMT(0.005, 180, 100000)

The spreadsheet will return:

• -843.86

The correct understanding:

• -843.86 is just how the software displays the expense.

• The actual monthly mortgage payment is 843.86

Why is analyzing these results so important?

• Helping you understand the correct monthly payment amount when taking out a mortgage.

• Avoid confusion when creating long-term financial plans.

• It's easy to compare different loan scenarios by varying the interest rate or loan term.

Tip 2: How to calculate mortgage interest using a simple formula

Step 1: Understand the formula for calculating monthly mortgage payments.

Formula for calculating monthly mortgage payments
The monthly payment amount is determined by the following formula:

• M = P × r × (1 + r)ⁿ / [(1 + r)ⁿ − 1]

This is the standard formula used by banks and financial experts to calculate monthly mortgage payments .

The meaning of each variable in the formula
Each symbol in the formula represents a key element of the loan:

• M : The amount to be paid each month, including principal and interest.

• P : Initial loan amount (principal of mortgage loan)

• r : Monthly loan interest rate

  • Calculated by dividing the annual interest rate by 12.

• n : Total number of repayment periods

  • That is the total number of months you have to pay back the loan.

Why should we understand this formula?
Understanding the formula will help you:

• Understand how banks calculate monthly payments.

• Check the results from Excel or an online calculator.

• Proactively estimate your repayment amount when interest rates or loan terms change.

• Avoid confusion when comparing bank mortgage loan packages.

Step 2: How to enter data into the formula to calculate mortgage payments

Prepare the information before calculating.
You need three basic pieces of information, usually available in your loan agreement or loan quote from the bank:

• Loan amount (P) : the actual principal amount you borrow

• Monthly interest rate (r) : converted from annual interest rate

• Total number of repayment periods (n) : total number of months to repay the loan

Before incorporating the figures into the formula, double-check them to ensure accuracy and avoid confusing annual and monthly interest rates.

An easy-to-understand example.
Let's say you take out a mortgage with the following conditions:

• Loan amount: 100,000

• Annual interest rate: 6%

• Loan term: 15 years

How to identify each variable:

• P = 100,000

  • This is the initial loan amount.

• r = 0.005

  • Calculation method: 6% ÷ 12 = 0.5% → 0.5% ÷ 100 = 0.005

• n = 180

  • Calculation method: 15 × 12 = 180 months

Enter the data into the calculation formula.
When we substitute the above values ​​into the formula, we get:

• M = 100,000 × [0.005 × (1 + 0.005)¹⁸⁰] / [(1 + 0.005)¹⁸⁰ − 1]

The result is the amount you have to pay each month when you take out a mortgage , including both principal and interest.

Why should we practice this step?

• Understanding the nature of mortgage interest rate calculation

• Proactively verify the figures provided by the bank.

• It's easy to estimate your repayment when interest rates or loan terms change.

• Avoid borrowing beyond your actual financial means.

Step 3: Simplify the formula by adding 1 to r.

Perform the first calculation in parentheses.
Following the correct order of operations, you need to process the part in parentheses first, that is, add 1 + r to both the numerator and the denominator.

• r is the monthly loan interest rate.

• Adding 1 to r simplifies the exponential expression that follows.

• The recipe will become more intuitive and easier to follow.

Applying it to a real-world example.
With the available data:

• P = 100,000

• r = 0.005

• n = 180

We do the following:

• 1 + r = 1 + 0.005 = 1.005

The simplified formula
After this step, the formula for calculating monthly mortgage payments will become:

• M = 100,000 × [0.005 × (1.005)¹⁸⁰] / [(1.005)¹⁸⁰ − 1]

Why is this step important?

• It helps make formulas shorter, easier to read, and easier to calculate.

• Reduce the risk of errors when using a calculator.

• Convenient for comparing results with those from Excel or online calculators.

• Helping beginners better understand how to calculate mortgage interest rates step-by-step.

Step 4: Calculate the exponent in the mortgage loan formula.

Identify the part for which to calculate the power.
Only the value (1 + r) is raised to the power of n .

• r: monthly loan interest rate

• n: total number of repayment periods (total number of loan months)

• The other parts of the formula are not raised to a power.

In the example under consideration:

• 1 + r = 1.005

• n = 180

How to calculate the power of (1 + r)ⁿ
You can choose one of the following options:

• Use a calculator with a power (xʸ) button.

  • Input: 1,005

  • Press the xʸ button

  • Input: 180

  • Press =

• Or use Google

  • Type: 1.005^180

  • Google will provide the results immediately.

The results are illustrated in the example.
The value obtained is:

• (1,005)¹⁸⁰ ≈ 2,454

Update the formula after calculating the exponent.
After this step, the formula for calculating monthly mortgage payments will become:

• M = 100,000 × [0.005 × 2.454] / (2.454 − 1)

Important notes to avoid mistakes.

• Only the part (1 + r) is raised to a power.

• Do not raise to the power of:

  • r stands before the parentheses

  • The number -1 at the end of the denominator

• Entering the exponent in the wrong position will cause the result to be significantly off.

Step 5: Further simplify to arrive at the most concise formula.

Processing the numerator (above)
In the numerator, you multiply the monthly interest rate r by the power you just calculated.

• r = 0.005

• (1 + r)ⁿ = 2.454

• Operation:

  • 0.005 × 2.454 = 0.01227

Processing the denominator (below)
In the denominator, simply subtract 1 from the power of the result.

• 2,454 − 1 = 1,454

The simplified formula
At this point, the formula for calculating monthly mortgage interest has become very simple:

• M = 100,000 × (0.01227 / 1.454)

Why is this step so important?

• Makes formulas easier to read and calculate using a regular calculator.

• Avoid confusion when working with exponents and parentheses.

• Convenient for comparing results with Excel or online calculators.

• Suitable for those who want to understand how banks calculate monthly payments.

Step 6: Perform the division to determine the payment coefficient.

How to perform division
You take the top part of the formula and divide it by the bottom part:

• Numerator: 0.01227

• Sample number: 1,454

• Operation:

  • 0.01227 ÷ 1.454 = 0.008439

The result is a small decimal number, reflecting the monthly repayment rate relative to the loan amount.

Update the formula after dividing.
After this step, the formula for calculating monthly mortgage payments is rewritten concisely as follows:

• M = 100,000 × 0.008439

The meaning of the number just calculated

• 0.008439 is the coefficient used to calculate the monthly payment.

• By multiplying this factor by the loan amount, you'll get the monthly payment.

• This is how banks and financial institutions determine the periodic mortgage payment.

Why is it necessary to clarify this step?

• This helps you understand how your monthly payments are calculated.

• It's easy to check the results from Excel or an online calculator.

• Proactively estimate your repayment amount when interest rates or loan terms change.

Step 7: Multiply by the loan amount to get the monthly payment.

Perform the final multiplication.
You take P (the loan amount) and multiply it by the result calculated in the previous step.

• P = 100,000

• Payment ratio = 0.008439

• Operation:

  • 100,000 × 0.008439 = 843.90

How should you interpret the results?

• 843.90 is the amount to be paid each month.

• This figure includes:

  • Principal

  • Mortgage interest

• This is a fixed monthly payment obligation throughout the loan term (if the interest rate remains unchanged).

Why is this result so important?

• It helps you know exactly how much money you need to prepare each month.

• It serves as a basis for assessing the ability to obtain a home loan.

• It's easy to compare different loan options by changing the interest rate or loan term.

• Avoid falling into a state of prolonged financial pressure.

Tip 3: How to create a mortgage loan installment schedule using Excel

Step 1: Set up a mortgage amortization schedule.

What is a loan depreciation schedule used for?
An amortization schedule gives you a detailed overview of the entire loan lifecycle.

• Know the exact interest and principal amounts for each repayment period.

• Track your decreasing outstanding balance over time.

• It's easy to calculate if you want to pay off your debt early.

• Understanding the nature of how banks calculate mortgage interest rates is crucial.

1. Enter the basic loan information into the spreadsheet.
Open Excel or Google Sheets and start entering the background information in the upper left corner of the table.

• Cell A1: Record the annual loan interest rate.

  • Cell B1: Enter the annual interest rate (e.g., 6%)

• Box A2: Record the loan term (years)

  • Cell B2: Enter the number of years for the loan (e.g., 15)

• Cell A3: Record the number of installments per year

  • Box B3: Enter 12 (if paying monthly)

• Cell A4: Record the initial loan amount.

  • Cell B4: Enter the loan amount (e.g., 100,000)

2. Why should I enter information this way?
This presentation method helps:

• It's easy to review the data when interest rates or loan terms change.

• Conveniently link the formula to the depreciation table below.

• Avoid confusing annual interest rates with monthly interest rates.

• In accordance with the standard mortgage depreciation schedule of banks.

Important note before proceeding

• Always enter the interest rate in the correct unit (yearly or monthly).

• Double-check all the data before performing calculations.

• A small discrepancy can significantly alter a mortgage interest rate spreadsheet.

Step 2: Create columns for the mortgage loan depreciation table.

1. Leave enough space for the board to be easily visible.

• Leave a blank line right below the loan information section.

• This makes the table clear, easy to read, and avoids formula confusion.

2. Create column headers in the depreciation table.
In row 6 of the spreadsheet, enter the headings from column A to column E as follows:

• Column A: Number of payment installments

  • Show the monthly repayment schedule.

• Column B: Monthly payment amount

  • It is a fixed payment that has been calculated in advance.

• Column C: Principal amount repaid during the period

  • The amount of money that reduces the outstanding balance.

• Column D: Interest paid during the period

  • Interest is calculated on the remaining balance.

• Column E: Remaining balance

  • The amount of loan that remains unpaid after each installment.

Why are these columns needed?

• It helps you see clearly how much principal and interest you pay each month.

• Accurately track decreasing outstanding balances over time.

• It is easy to analyze the impact of interest rates on the total amount payable.

• It is very helpful to consider paying off debt early or refinancing.

Step 3: Fill in the data for the first month in the mortgage depreciation schedule.

1. Enter the number of the first payment installments.

• In cell A7 , enter:

  • 1

• This number represents the first payment installment (January).

2. Calculate the monthly payment amount.
In the Monthly Payment Amount column (cell B7), enter the formula:

• =PMT(B1/B3, B2*B3, B4)

Meaning:

• B1/B3: monthly loan interest rate

• B2*B3: total number of repayment installments

• B4: Initial loan amount

This is the PMT function , used to calculate monthly mortgage payments.

3. Calculate the principal payment for the month.
In the "Principal Amount Paid During Period" column (cell C7), enter:

• =PPMT(B1/B3, A7, B2*B3, B4)

Meaning:

• The PPMT function indicates the portion of the principal paid in the first month.

• A7 is the number of periods being calculated (January).

4. Calculate the interest payable for the month.
In the column for Interest paid during the period (cell D7), enter:

• =IPMT(B1/B3, A7, B2*B3, B4)

Meaning:

• The IPMT function shows the mortgage interest payable for that month.

• This is the part most people are most interested in when tracking borrowing costs.

5. Calculate the remaining balance after the first month.
In the Remaining Balance column (cell E7), enter:

• =(B4 + C7)

Note:

• Since the principal payment in C7 is negative, adding it to B4 will result in a new outstanding balance.

• The result reflects the remaining loan amount after the first month's payment.

Why is this step so important?

• It helps you clearly see how your monthly payments are allocated.

• Understanding exactly how mortgage interest is calculated on a monthly basis.

• It serves as a foundation for extending the formula to subsequent months.

• It is very useful when you want to analyze the total interest payable over the loan period.

Step 4: Complete the mortgage loan depreciation schedule.

Drag the formula to the entire loan term.
Here's what you do:

• Select the area from cell A7 to cell E7 (the row for the first month).

• Scroll down with your mouse until you reach the last payment due date.

• The number of lines to pull is:

  • Number of loan years × number of repayments per year

  • Example: 15 years × 12 months = 180 lines

After pulling is complete:

• The "Remaining Balance" column (column E) in the last row must equal 0.

• This indicates that the loan has been repaid correctly according to the mortgage interest calculation method.

Check and fix any errors if the payment number does not increment automatically.
In some cases, the "Number of Payments" column doesn't automatically increment when you scroll down. You can fix this very quickly:

• In cell A8 , enter the formula:

  • =(A7+1)

• Then drag this formula down to the last line.

When the payment number is updated correctly:

• The remaining columns (principal, interest, outstanding balance) will be automatically recalculated accurately.

Why is it necessary to complete a depreciation schedule?

• It helps you see clearly how much interest and principal you pay each month.

• Accurately track your remaining balance over time.

• It's easy to calculate the total interest payable on the entire loan.

• It's very helpful to consider paying off your debt early or adjusting your financial plan.

Use an online mortgage calculator for the quickest and easiest way.

How to use an online mortgage calculator
You just need to search for common phrases like "mortgage loan calculator" or "mortgage loan calculator" on Google. Most tools will ask you to enter some basic information:

• Loan term (number of years)

• Annual loan interest rate

• Initial loan amount (principal)

After entering the information:

• Press the “Calculate” button.

• The system will return:

  • Amount to be paid each month

  • Total interest payable

  • Total amount payable throughout the loan term.

Why should you use an online tool to calculate mortgage interest rates?

• No need to understand complicated formulas.

• Results available in seconds.

• Suitable for first-time homebuyers.

• Easy to check and compare with the figures provided by the advising bank.

Note regarding additional monthly payments
Depending on the terms of your mortgage loan agreement, you may be permitted to:

• Pay more than the minimum amount each month.

• Use the extra payment to:

  • Reduce interest rates.

  • Reduce principal amount

  • Shorten the loan term.

Before applying, you should contact the bank or lender directly to confirm:

• Will there be a penalty for early repayment?

• The additional payment is deducted from the principal or interest.

Compare online loan options using a calculator.
Online mortgage calculators are especially useful when you need to compare different loan options.

For example:

• 15-year loan with 6% interest rate

• 30-year loan with 4% interest rate

Simply enter the options one by one, and you'll easily realize:

• Although the interest rate on a 15-year loan is higher, the overall cost is lower.

• Long-term loans make monthly payments easier, but the total interest is much higher.

References

1. http://www.investopedia.com/terms/m/mortgage.asp
2. http://www.mtgprofessor.com/formulas.htm
3. http://www.excel-easy.com/examples/loan-amortization-schedule.html
4. http://www.bankrate.com/calculators/
   mortgages/mortgage-payment-calculator.aspx

Translated by: Rene Lee Nguyen .