How to Calculate Principal and Interest

If you own a home plate, you credibly know that a fortune of what you pay the lender each calendar month goes toward the original loan measure while some gets applied to the concern. But figuring out how banks actually divvy those up can seem confusing.

You may besides wonder why your payment stays signally coherent, even though your outstanding balance keeps going down. If you understand the basic concept of how lenders calculate your payment, however, the process is simpler than you might think.

Key Takeaways

  • Mortgage payments are made up of two components. The principal is the amount of the loan itself and the interest is the monthly amount that the lender charges you on top of the principal. 
  • With fixed-rate mortgages, your monthly payment is consistent because of a process called amortization. 
  • In addition to the principal and interest that you pay the lender, your monthly payment may also include other expenses such as mortgage insurance premiums and taxes held in escrow. 

Principal and Interest

Each mortgage payment that you make is made up of two main components : principal and concern.


The star is the original lend sum not including any interest. For model, let ‘s suppose you purchase a $ 350,000 home and put down $ 50,000 in cash. That means you ’ re borrowing $ 300,000 of principal from the lender, which you ‘ll need to pay back over the length of the loan. however, the bank besides charges a tip for lend you those funds, which is represented by the interest assign of your requital .


Sticking with our example, let ’ s say the loanword is a 30-year mortgage with a 4 % annual interest rate. Since you ’ rhenium making monthly, rather than annual, payments throughout the class, the 4 % matter to rate gets divided by 12 and multiplied by the outstanding principal on your lend. In this model, your first monthly requital would include $ 1,000 of pastime ( $ 300,000 x 0.04 annual interest rate ÷ 12 months ) .

If you plug your purchase monetary value, your down payment, the length of your loan, and your APR ( see more on this below under “ Interest Rate vs. APR ” ) into the Investopedia Mortgage Calculator, you will see that your monthly payments to the lender would equal $ 1,432.25. As we noted earlier, $ 1,000 of your first payment rigorously covers the concern cost, meaning the remaining $ 432.25 is paying down your outstanding lend poise or principal .

Of course, the model above does n’t include other costs, such as mortgage indemnity and property taxes held in escrow, which are not paid to the lender.

How Amortization Works

You may be wondering why your mortgage payment—if you have a fixed-rate loan —stays the same from one calendar month to the adjacent. In hypothesis, that sake rate is being multiplied by a shrink star balance. so shouldn ’ t your monthly circular get smaller over prison term ?

The reason that ’ s not the case is that lenders use amortization when calculating your payment, which is a room of keeping your monthly bill consistent. As a leave, your monthly requital is comprised of by and large interest in the early years with a smaller assign of the payment going towards reducing the principal .

example of Amortization

Assuming you don ’ thymine refinance, your loanword payment will be the same 15 years belated. But by now, you ’ ve chipped away at your principal remainder. In 15 years, you would have a remaining balance of approximately $ 193,000 of the principal on your loan .

Multiplying $ 193,000 by the interest rate ( 0.04 ÷ 12 months ), the matter to part of the payment is now merely $ 645.43. however, you ’ re paying off a bigger part of the principal, meaning $ 786.82 of the $ 1,432.25 monthly payment is going towards the chief .

The table below shows the monthly payments at versatile points in the 30-year mortgage. You ‘ll notice that the pastime helping of the monthly payment declines while the star helping increases over the life of the lend .

Mortgage Loan Amortization with Principal and Interest Breakdown
 Year  Principal  Interest Monthly Payment
Year One  $432.25  $1,000 $1,432.25
 15 Years  $786.82 $645.43  $1,432.25
 20 Years  $960.70  $471.54 $1,432.25
 30 Years $1,427.49   $4.76 $1,432.25

During the last year of your mortgage, you ’ re paying off by and large principal and identical little concern. By leveling out your payments like this, lenders are making your payments more accomplishable. If you paid the lapp amount in principal over the course of the loanword, you ’ d have to make much higher monthly payments right after taking out the loan and those amounts would plummet at the chase end of the repayment.

If you ’ re wondering how much you ’ ll yield toward principal versus sake over time, the Investopedia Mortgage Calculator besides shows the breakdown of your payments over the length of your lend.

Adjustable-Rate Mortgages

If you take out a fixed-rate mortgage and entirely pay the sum due, your entire monthly requital will stay the same over the course of your loanword. The part of your requital attributed to matter to will gradually go down, as more of your payment gets allocated to the star. But the total come you owe won ’ t change .

however, it doesn ’ deoxythymidine monophosphate work that way for borrowers who take out an adjustable-rate mortgage, or ARM. They pay a given concern pace during the initial period of the lend. But after a certain length of time—say, one year or five years, depending on the loan—the mortgage “ resets ” to a modern interest pace. Often, the initial rate is set below the grocery store rate at the time you borrow, and then increases following the reset .

on the spur of the moment, you ’ ll detect that your monthly requital has changed. That ’ south because your outstanding principal is being multiplied by a different ( normally higher ) interest rate.

interest Rate vs. APR

When receiving a loanword offer, you may come across a term called the annual percentage rate, or APR. The APR and the actual interest pace that the lender is charging you are two offprint things, so it ’ second significant to understand the distinction .

Unlike the interest pace, the APR factors in the full annual cost of taking out the loan, including fees such as mortgage insurance, dismiss points, loan initiation fees and some close costs. It averages the full monetary value of borrowing over the duration of the lend .

It ’ second significant to realize that your monthly payment is based on your interest rate, not the annual percentage rate. however, lenders are required by law to disclose the APR on the loan estimate they provide after you submit an application, so that you can have a more accurate word picture of how much you ’ re actually paying to borrow that money.

Some lenders may charge you a lower interest rate but charge higher upfront fees, then including the APR helps provide a more holistic comparison of different lend offers. Because the APR includes associated fees, it ’ south higher than the actual sake rate .

How Is My Interest Payment Calculated?

Lenders multiply your great balance by your annual interest rate, but watershed by 12 because you ’ rhenium making monthly payments. so if you owe $ 300,000 on your mortgage and your rate is 4 %, you ’ ll initially owe $ 1,000 in interest per month ( $ 300,000 x 0.04 ÷ 12 ). The rest of your mortgage payment is applied to your principal .

What Is Amortization?

Amortizing a mortgage allows borrowers to make pay back payments on their loan, even though their outstanding balance keeps getting lower. early on, most of your monthly payment goes toward interest, with alone a minor percentage reducing your principal. At the tail end of refund, that switches—more of your requital reduces your great balance and lone a small percentage of it covers concern .

What’s the Difference Between Interest Rate and APR?

The sake rate is the total that the lender actually charges you as a percentage of your lend amount. By contrast, the annual share rate, or APR, is a direction of expressing the total cost of borrowing. consequently, APR incorporates expenses such as loan initiation fees and mortgage policy. Some loans offer a relatively first gear interest rate, but have a higher APR because of early fees.

The Bottom Line

You probable know how much you ‘re paying to the mortgage servicer each month. But figuring out how that money is divided between principal and interest can seem cryptic. In fact, figuring out how much you ‘re paying in matter to is equally simple as multiplying your pastime rate by your outstanding balance and separate by 12. It ‘s only because lenders adjust the total credited to your original loanword balance that your payments stay unusually coherent over the years.

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Category : Finance

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