Loan Calculator

The Loan Payment Formula (With Worked Examples)

Every amortizing loan payment comes from one core equation. The monthly payment formula is:

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

Where:
  M = monthly payment
  P = principal (loan amount)
  r = monthly interest rate (annual rate ÷ 12)
  n = total number of payments (years × 12)

The monthly rate is the annual rate divided by 12, expressed as a decimal. A 6% annual rate becomes 0.06 / 12 = 0.005 per month.

Example 1: A $20,000 car loan at 6% for 5 years

P = 20,000
r = 0.06 / 12 = 0.005
n = 5 × 12 = 60

M = 20,000 × [0.005 × (1.005)^60] / [(1.005)^60 − 1]
(1.005)^60 = 1.34885
M = 20,000 × [0.005 × 1.34885] / [0.34885]
M = 20,000 × 0.0193328
M = $386.66 per month

Total paid = 386.66 × 60 = $23,199.60, so total interest = $3,199.60.

Example 2: The same loan stretched to 7 years

n = 7 × 12 = 84
(1.005)^84 = 1.52037
M = 20,000 × [0.005 × 1.52037] / [0.52037]
M = $292.19 per month

The payment drops to a comfy $292.19, but total interest jumps to $4,543.96 — over $1,300 more for the convenience of a lower monthly bill.

Example 3: A $250,000 mortgage at 7% for 30 years

P = 250,000, r = 0.07/12 = 0.0058333, n = 360
(1.0058333)^360 = 8.11640
M = 250,000 × [0.0058333 × 8.11640] / [7.11640]
M = $1,663.26 per month

Over 30 years you'd pay about $598,772 total, meaning roughly $348,772 in interest — more than the house itself. That single number is why term and rate matter so much on large loans.

Interest Rate vs. APR: The Comparison That Trips People Up

Borrowers constantly confuse the interest rate with the APR (Annual Percentage Rate), and lenders don't always make the distinction obvious.

• •Interest rate is the cost of borrowing the principal, expressed as a yearly percentage. It's what the payment formula uses.
• •APR rolls the interest rate plus fees (origination fees, points, some closing costs) into a single annualized figure. APR is always equal to or higher than the interest rate.

Because APR includes fees, it's the better number for comparing two loan offers. A loan with a lower rate but heavy fees can have a higher APR than a loan with a slightly higher rate and no fees.

A quick illustration

Suppose two lenders offer $20,000 for 5 years:

• •Lender A: 6.0% rate, $600 origination fee → APR ≈ 7.1%
• •Lender B: 6.4% rate, no fees → APR ≈ 6.4%

Lender A looks cheaper on the sticker rate, but Lender B is actually the better deal once fees are baked in. Always compare APR to APR.

There's also simple interest vs. compound interest. Most amortizing loans use simple interest calculated on the outstanding balance each period — you're not charged interest on interest as long as you pay on time. Credit cards and some other products compound, which is far more expensive. This calculator models the standard amortizing (simple-interest-on-balance) structure used by auto, personal, and mortgage loans.

Typical Loan Rates and Terms by Category

Rates vary enormously by loan type, your credit score, and market conditions. The table below shows representative U.S. ranges as a planning benchmark — always confirm current rates with lenders.

How credit score moves your rate

Moving from "fair" to "excellent" credit can shave several percentage points off your rate — on a large loan, that's often more money than any coupon or discount you'll ever clip.

Reading Your Amortization Schedule

An amortization schedule is a payment-by-payment breakdown showing how each payment is split between interest and principal, and how the balance shrinks to zero. Early on, most of your payment is interest; over time, the balance tips toward principal.

Here's the first few months of the $20,000, 6%, 5-year loan (payment $386.66):

How each row is built:

Interest = Remaining Balance × monthly rate (0.005)
Principal = Payment − Interest
New Balance = Remaining Balance − Principal

Notice in month 1 that $100 of your $386.66 evaporates as interest, and only $286.66 reduces your debt. This is why paying a little extra toward principal early has an outsized effect — every extra dollar skips all the future interest that dollar would have generated.

The steady shift from interest-heavy to principal-heavy payments is called amortization, and understanding it is the single best defense against feeling like your balance "never goes down" in the first year.

How to Use This Loan Calculator

The calculator is built around three inputs and a set of instant outputs.

Inputs

• •Loan amount (principal): The total you're borrowing. For a purchase, this is the price minus your down payment. Don't forget to add taxes and fees if they're being financed.
• •Interest rate: Enter the annual rate your lender quoted (e.g., 6.5). If you only have the APR, using it gives a slightly conservative, safe estimate.
• •Loan term: How long you have to repay, in years or months. Common terms are 36, 48, 60, or 72 months for autos and 15 or 30 years for mortgages.

Outputs

• •Monthly payment: Your fixed payment each period — the headline number.
• •Total interest: Everything you'll pay beyond the principal.
• •Total cost: Principal + total interest, i.e., the true price of borrowing.
• •Amortization schedule: The full month-by-month table of interest, principal, and balance.

A practical workflow

1. •Enter the amount, rate, and term of the offer you're considering.
2. •Note the monthly payment — can your budget absorb it comfortably (ideally under ~15% of take-home pay for a car, ~28% for housing)?
3. •Change the term to see the trade-off between monthly affordability and total interest.
4. •Try a rate that reflects your actual credit band, not the advertised "best" rate.
5. •Use the schedule to see how quickly you'd build equity or pay down the balance.

Smart Strategies to Pay Less Interest

Small changes to how you structure and repay a loan can save real money. Here are the highest-leverage moves:

• •Shorten the term if you can afford it. A 15-year mortgage versus a 30-year at the same rate can cut total interest by more than half. The monthly payment is higher, but far less goes to the lender.
• •Make extra principal payments. Even one extra payment a year, or an extra $50/month, meaningfully shortens the loan. On the $250k mortgage above, an extra $200/month can cut roughly 6–7 years and tens of thousands in interest.
• •Round up your payment. Paying $400 instead of $386.66 quietly accelerates payoff with money you barely notice.
• •Refinance when rates drop. If market rates fall 1%+ below your current rate and you'll keep the loan a while, refinancing can be worth the closing costs.
• •Improve your credit before you borrow. A better score means a lower rate. On big loans, spending a few months boosting your score can outperform any negotiation at the dealership.
• •Bi-weekly payments. Paying half your monthly amount every two weeks results in 26 half-payments = 13 full payments a year instead of 12, sneaking in one extra payment annually.

When a longer term makes sense: If a shorter term would strain your budget to the point of risking a missed payment, the lower monthly payment of a longer term can be the responsible choice — as long as you understand the interest cost and aim to prepay when you can.

Common Loan Mistakes to Avoid

Even careful borrowers fall into predictable traps. Here are the big ones, with the fix for each:

• •Shopping by monthly payment instead of total cost. Dealers love the question "What payment fits your budget?" because a low payment can hide a long term and a fat interest bill. Fix: Always check total cost and total interest, not just the monthly figure.
• •Ignoring APR and fees. Comparing sticker rates alone can lead you to a pricier loan. Fix: Compare APR to APR across offers.
• •Confusing rate with term impact. A lower rate on a much longer term can still cost more overall. Fix: Hold the term constant when comparing rates.
• •Forgetting the down payment reduces principal. A bigger down payment shrinks the amount you finance and every dollar of interest on it. Fix: Model different down payments in the calculator.
• •Assuming you can't prepay. Most modern consumer loans have no prepayment penalty, but a few do. Fix: Confirm before signing, then prepay freely.
• •Overlooking add-on products. Extended warranties, gap insurance, and credit insurance are often rolled into the financed amount, quietly inflating your principal and interest. Fix: Decide on these separately and know their true cost.

Myth: "A 0% financing offer is always the best deal." Not necessarily — sometimes taking a cash rebate and financing elsewhere at a low rate beats 0% financing that requires forgoing the rebate. Run both scenarios through the calculator before deciding.