How To Calculate Interest on a Personal Loan: Quick Guide

Understanding how to calculate interest on a loan is essential for making smart financial decisions. Whether you’re planning to finance a car, pay for college or secure a mortgage, interest is a significant part of what you’ll owe.

Need help finding the right loan? MoneyLion can connect you with personalized loan offers up to $50,000. Compare interest rates, terms, and fees from multiple lenders to secure the best option for your needs.

MoneyLion

What’s a simple way to avoid interest on purchases?

Pay minimum onlySkip due datesUse multiple cardsPay balance in full

54

Key Takeaways

• Loan interest is calculated using two main methods: simple interest and amortized interest. Simple interest applies a fixed percentage to the original principal, while amortized interest recalculates monthly based on the remaining balance.

• With amortized loans, early payments go mostly toward interest rather than principal. This is standard for mortgages, auto loans, personal loans and student loans, meaning you pay more interest upfront and more principal over time.

• Your credit score, debt-to-income (DTI) ratio, loan amount and repayment term all affect the interest rate you're offered. Borrowers with strong credit and lower debt loads typically qualify for the most favorable rates.

Summary generated by AI, verified by MoneyLion editors

How To Calculate Interest on a Loan?

To understand the total cost of a loan, you'll have to understand these terms:

• Principal: The amount borrowed

• Interest rate: The percentage charged by the lender

• Loan term: The length of time to repay the loan

• Repayment structure: How payments are allocated to principal and interest

There are two common types of interest: simple interest and amortized interest.

Simple Interest 

Simple interest is a basic way of calculating loan interest where you pay a fixed percentage of the original loan amount (principal), regardless of how much you’ve already paid back.

Unlike compound interest, it doesn’t charge interest on previously accumulated interest.

Understanding how to calculate the percentage interest on a loan is straightforward with the simple interest formula:

• Principal × Rate × Time

For example, if you borrow $10,000 at a 5% annual interest rate for three years:

• $10,000 × 0.05 × 3 = $1,500

You’d pay $1,500 in interest over the life of the loan. Simple interest is typically used for short-term loans and some auto loans.

Amortized Interest

Amortized interest is where each fixed monthly payment includes both principal and interest. This system, which allocates a larger portion toward interest early in the loan and gradually shifts toward principal over time, is common for long-term or larger loans like mortgages, car loans and student loans. 

Unlike simple interest, which charges a consistent interest amount based on the original loan balance, amortized interest recalculates the interest portion each month based on the remaining principal balance.

Amortized loans are a more complex way to calculate interest on loan payments, and it can be helpful to use a calculator or an amortization table to understand how payments break down.

Take a look at an example of an amortization schedule for a $5,000 personal loan at a 5% annual interest rate (0.417% monthly) for 12 months:

Personal Loans 

Interest rates for personal loans are typically amortized and can vary widely based on factors like your credit score, the amount you borrow, and how long you take to repay it.

On average, rates range from 6% to 36%, with lower rates typically reserved for borrowers with excellent credit.

When considering getting a personal loan, understand whether the loan has a fixed or variable interest rate.

• Fixed rates: Provide predictable monthly payments, making budgeting easier.

• Variable rates: May fluctuate over time, potentially increasing your costs.

If you’re planning to borrow, take the time to understand how personal loans work and compare lenders to find the best rates and terms. 

For those aiming to minimize costs, it’s worth exploring options for a low-interest personal loan.

Remember, the formula to calculate interest on a loan is:

• Interest = Principal × Rate × Time

Student Loans

Student loans also tend to have amortized interest. With federal loans, the type of loan determines when interest begins to accrue. For example:

• Subsidized loans: The government covers the interest while you’re in school and during deferment periods.

• Unsubsidized loans: Interest starts accruing from the day the loan is disbursed, even if you’re still in school.

Private loans, on the other hand, often work differently. They may have fixed or variable interest rates, and terms vary by lender. This flexibility can be helpful, but it also means it’s important to know when interest starts adding up and how much you’ll owe.

For those wondering how to calculate student loan interest, it’s typically done daily based on the outstanding balance and interest rate. This means that paying extra whenever possible can reduce your total interest costs over time. 

Car Loans 

Interest on car loans is also amortized and depends heavily on your credit score and the lender’s terms. Borrowers with strong credit may qualify for lower interest rates or even promotions like 0% annual percentage rate (APR), while those with lower scores might face higher rates.

To calculate interest on auto loans, it’s helpful to use an auto loan interest calculator and factor in the loan term and vehicle price.

If you’re planning to buy a car soon, understanding market trends, such as when car interest rates might go down, can help you time your purchase for the best deal.

Mortgages

Mortgages also use amortized payments, where interest is higher in the early years.

• Fixed-rate mortgages: Provide homeowners with consistent monthly payments.

• Adjustable-rate mortgages (ARMs): Can start with lower rates but adjust over time based on market conditions.

If you’re considering a mortgage, understanding when to lock in a favorable rate could save you money over the long term. Monitoring trends, like whether interest rates might go down, can also help you decide the best time to act.

For those looking to save, there are strategies to secure a lower mortgage rate, ensuring affordability throughout the life of the loan.

Home Equity Loans

Home equity loans are amortized similarly to a standard mortgage. These loans allow you to borrow a lump sum against the equity built up in your home. They come with fixed interest rates, which means predictable monthly payments over the life of the loan.

They’re ideal for large, one-time expenses like renovations or consolidating higher-interest debt.

Home Equity Lines of Credit (HELOCs)

HELOCs are also amortized and work like a revolving credit line, letting you borrow as needed against your home’s equity. HELOCs typically have variable interest rates, meaning your payments can fluctuate based on market conditions.

When deciding between a HELOC and a personal loan, consider your borrowing needs. HELOCs provide flexibility for ongoing expenses, while personal loans are better suited for fixed amounts with stable repayment terms.

What Are the Factors That Affect Interest on Your Loan?

Your loan’s interest rate isn’t set in stone. Several factors influence how much interest you’ll pay:

• Credit score: A higher score typically means lower rates. Check your credit report for errors and work on improving your score before applying.

• DTI ratio: This measures your monthly debt payments against your income. Lenders prefer a lower ratio so try to reduce your debt to improve this metric.

• Loan amount: Larger loans may have higher rates, reflecting greater risk to the lender. Borrow only what you truly need.

• Loan term: Longer terms reduce monthly payments but increase total interest. Choose the shortest term you can afford.

• Type of loan: Secured loans usually offer lower rates than unsecured loans. Consider using collateral to secure better terms.

Making Sense of Loan Interest

Whether you’re dealing with personal loans, car loans, mortgages or home equity lines of credit, knowing how interest is calculated and how different factors affect your rate can help you make informed decisions.

From simple interest to amortized schedules, taking the time to grasp these concepts will empower you to optimize your borrowing experience.

FAQs

What is simple interest vs. compound interest?

Simple interest is calculated only on the loan principal, while compound interest is calculated on both the principal and the accumulated interest over time.

What is the formula for calculating loan interest?

The formula for simple interest is: Principal × Rate × Time. For compound interest, it includes accrued interest as part of the calculation.

Does the interest rate affect your monthly loan payment?

Yes, a higher interest rate increases your monthly payment, while a lower rate reduces it.

How is interest calculated on a mortgage loan?

Mortgage interest is typically amortized, with early payments going mostly toward interest and later payments focusing more on the principal.

Key Terms

• Principal: The original amount borrowed, not including interest or fees. Interest is calculated as a percentage of the principal, so borrowing only what you need helps keep total interest costs down.

• Simple interest: A method of calculating interest based solely on the original principal balance. It does not compound, making it straightforward to calculate using the formula: Principal x Rate x Time.

• Amortization: A repayment structure where fixed monthly payments are split between principal and interest, with a larger share going toward interest early in the loan term and shifting toward principal over time.

• Fixed interest rate: An interest rate that stays the same for the life of the loan, resulting in predictable monthly payments. Most personal loans and mortgages offer fixed-rate options.

• ARM: A home loan that starts with a fixed interest rate for an initial period, then adjusts periodically based on market conditions. Monthly payments can rise or fall after the fixed period ends.

Summary generated by AI, verified by MoneyLion editors

Sources

• Federal Reserve Bank of St. Louis. 2026. "Finance Rate on Personal Loans at Commercial Banks, 24 Month Loan."

• Consumer Financial Protection Bureau. 2023. "What is a debt-to-income ratio?"

• Consumer Financial Protection Bureau. 2025. "What is the difference between a fixed-rate and adjustable-rate mortgage (ARM) loan?"