Amortization Calculator — Full Payment Schedule
Generate a complete month-by-month amortization schedule for any loan. See exactly how much principal and interest you pay each month, your remaining balance, and the total cost of the loan over its full term.
Quick Presets
What Is the Amortization Calculator — Full Payment Schedule?
This amortization calculator generates a complete month-by-month payment schedule for any fixed-rate loan. It shows the exact split between principal and interest for every payment, the remaining balance after each payment, and the total cost of the loan — including how extra monthly payments can cut years off your term and save thousands in interest.
- ›Full amortization table — every payment broken into principal, interest, extra payment, and remaining balance, toggled between monthly and annual view.
- ›Balance vs interest chart — an SVG area chart showing your remaining balance decreasing and cumulative interest growing over the life of the loan.
- ›Extra payment analysis — enter an extra monthly principal payment to see exactly how many months you save and how much interest you avoid.
- ›Halfway milestone — the calculator flags the exact month when cumulative principal paid exceeds 50% of the original loan, a key psychological milestone.
- ›Payoff date — calculated from your start month and year, showing the exact calendar month when your final payment is due.
Formula
Monthly Payment Formula
P = L × r × (1 + r)ⁿ / ((1 + r)ⁿ − 1)
Monthly Interest Charge
Interest_m = Balance_m × r
Monthly Principal Reduction
Principal_m = P − Interest_m
New Balance
Balance_{m+1} = Balance_m − Principal_m − Extra
| Symbol | Name | Description |
|---|---|---|
| P | Monthly Payment | Fixed amount paid each month — includes principal and interest |
| L | Loan Amount | The original amount borrowed (principal) |
| r | Monthly Rate | Annual interest rate divided by 12 divided by 100 (e.g. 6%/12 = 0.005) |
| n | Number of Payments | Total months in the loan term (e.g. 30 years = 360 payments) |
| Extra | Extra Payment | Optional additional principal payment made each month |
| Balance | Remaining Balance | Unpaid principal — decreases with each payment |
How to Use
- 1Enter loan amount: Type the total amount you are borrowing. Use presets for common loan types: 30-year mortgage, 15-year mortgage, auto loan, or personal loan.
- 2Enter annual interest rate: Type the APR (annual percentage rate) as a percentage, e.g. 6.5 for 6.5%. This is the rate from your loan offer, not the monthly rate.
- 3Set the loan term: Enter the repayment period. Toggle between years and months — a 30-year mortgage is 360 months. Auto loans are often 48 or 60 months.
- 4Add extra monthly payment (optional): If you plan to pay more than the minimum, enter the extra amount here. Leave at 0 to see the base schedule. The calculator shows time and interest saved.
- 5Set start month and year: Choose when your first payment is due. This determines the calendar payoff date shown in the results.
- 6Click Calculate: Results appear instantly: monthly payment, total interest, payoff date, and the full amortization schedule.
- 7Explore the schedule: Toggle between monthly and annual views. Watch the highlighted milestone row — that is where you start paying more principal than interest each month.
Example Calculation
$300,000 mortgage at 6.5% for 30 years — first 3 months
Given: L = $300,000 r = 6.5%/12 = 0.541667% n = 360
Monthly payment:
P = 300,000 × 0.005417 × (1.005417)³⁶⁰ / ((1.005417)³⁶⁰ − 1)
P = $1,896.20
── Month 1 ──────────────────────────────────
Interest = 300,000 × 0.005417 = $1,625.00
Principal = 1,896.20 − 1,625.00 = $271.20
Balance = 300,000 − 271.20 = $299,728.80
── Month 2 ──────────────────────────────────
Interest = 299,728.80 × 0.005417 = $1,623.53
Principal = 1,896.20 − 1,623.53 = $272.67
Balance = 299,728.80 − 272.67 = $299,456.13
── Month 3 ──────────────────────────────────
Interest = 299,456.13 × 0.005417 = $1,622.05
Principal = 1,896.20 − 1,622.05 = $274.15
Balance = 299,456.13 − 274.15 = $299,181.98
Total interest over 30 years: ~$382,632
Payoff requires 360 payments of $1,896.20
Notice the front-loading of interest
In Month 1, only $271.20 of the $1,896.20 payment reduces the loan balance — that is just 14.3%. The remaining 85.7% goes to interest. By Month 180 (year 15), the split is roughly 50/50. By Month 350, almost all of each payment is principal. This is the core feature of amortization.
Understanding Amortization — Full Payment Schedule
What Is Amortization?
Amortization is the process of paying off a loan through scheduled, fixed payments over a set period. Each payment covers the interest accrued since the last payment and reduces the outstanding principal. The word comes from the Latin mors (death) — amortization literally means "killing the debt" gradually over time.
The defining feature of an amortizing loan is that the payment amount stays constant, but the split between principal and interest shifts dramatically from one payment to the next. Early payments are mostly interest; later payments are mostly principal.
- ›Fixed-rate mortgages are the most common amortizing loan — 30 or 15-year terms are standard.
- ›Auto loans, personal loans, and student loans also amortize on the same mathematical principle.
- ›Interest-only loans and balloon loans do NOT amortize — they require a lump-sum final payment.
How the Payment Formula Works
The monthly payment formula P = L × r × (1+r)ⁿ / ((1+r)ⁿ − 1) is derived from the present value of an annuity. The idea: your lender gives you L dollars today, and you repay it as n equal monthly payments of P, each discounted at rate r. Setting the present value of all future payments equal to L gives the formula above.
Once the payment is fixed, the balance falls according to: Balance_m = L × ((1+r)ⁿ − (1+r)ᵐ) / ((1+r)ⁿ − 1). This elegant closed form means you can calculate the balance at any point without iterating through every prior payment.
Why the monthly rate matters
Lenders quote APR (annual percentage rate), but interest accrues monthly. The monthly rate is APR / 12 / 100. A 6% APR becomes r = 0.005 per month. Because interest compounds, the effective annual rate is (1 + 0.005)¹² − 1 = 6.168%, slightly higher than the stated APR. This compounding effect adds hundreds of dollars over the life of a long-term mortgage.
Front-Loading of Interest in Early Payments
The interest charged each month is a percentage of the remaining balance. Since the balance is highest at the start of the loan, the interest charge is also highest in early months. This creates the characteristic front-loading of interest:
| Payment Number | Principal Portion | Interest Portion | Balance Remaining |
|---|---|---|---|
| 1 | 14.3% | 85.7% | $299,729 |
| 60 | 20.9% | 79.1% | $279,163 |
| 120 | 30.7% | 69.3% | $248,609 |
| 180 | 45.2% | 54.8% | $204,123 |
| 240 | 66.4% | 33.6% | $137,963 |
| 300 | 97.6% | 2.4% | $43,212 |
Based on $300,000 at 6.5% APR, 30-year term.
The Impact of Extra Payments
Extra payments go entirely to principal, not interest. This has an outsized effect because every dollar of principal eliminated today eliminates all the future interest that would have accrued on it. An extra $200/month on a $300,000 30-year mortgage at 6.5% saves approximately $70,000 in interest and cuts the term by over 5 years.
- ›Even one extra payment per year (making 13 instead of 12) shortens a 30-year mortgage by ~4 years.
- ›Extra payments are most powerful early in the loan when the balance is highest.
- ›Always confirm with your lender that extra payments are applied to principal, not future interest.
- ›Some loans charge prepayment penalties — check your loan agreement before making extra payments.
Fixed-Rate vs ARM Amortization
This calculator models a fixed-rate loan where the interest rate and payment never change. An adjustable-rate mortgage (ARM) starts with a fixed period (e.g. 5 years) and then adjusts periodically based on a market index.
- ›Fixed-rate: Predictable payments. Rate does not change regardless of market conditions. Best when rates are low and you plan to hold long-term.
- ›ARM: Lower initial rate than a comparable fixed loan. Rate adjusts (usually annually) after the fixed period — payments can rise significantly. Best when you plan to sell or refinance before the adjustment period begins.
- ›Interest-only: Payments cover only interest during an initial period. No principal is reduced during this phase — the balance does not fall. Typically used for investment properties or short-term bridge financing.
Frequently Asked Questions
What is an amortization schedule?
An amortization schedule breaks down every loan payment into three components:
- ›Interest — the cost of borrowing, charged on the remaining balance
- ›Principal — the portion that reduces what you owe
- ›Remaining balance — how much you still owe after each payment
The schedule is especially useful for understanding how much of your early payments go to interest versus principal, and for planning extra payments strategically.
Why do I pay so much interest at the beginning of a mortgage?
Interest = Balance × monthly rate. At the start, the balance is the full loan amount, so interest is maximised. Each payment reduces the balance slightly, which reduces next month's interest charge by a tiny amount, freeing slightly more of the payment for principal. This positive feedback loop accelerates in the final years of the loan.
On a $300,000 30-year mortgage at 6.5%:
- ›Month 1: $1,625 interest, $271 principal (85.7% / 14.3%)
- ›Year 15, month 1: roughly $952 interest, $944 principal (50/50 crossover)
- ›Month 360: ~$10 interest, $1,886 principal
How much does an extra $200/month save on a 30-year mortgage?
Extra payments go entirely to principal. Every dollar of principal eliminated today eliminates all future interest that would have accrued on it. The savings are non-linear: extra payments made early in the loan save significantly more than the same payments made later.
- ›+$100/month on a 30yr at 6.5%: saves ~$35,000 and ~3 years
- ›+$200/month: saves ~$65,000–$75,000 and ~5–6 years
- ›+$500/month: saves ~$130,000+ and ~10+ years
Use this calculator's extra payment field to see the exact numbers for your loan.
What is the difference between APR and interest rate?
For this amortization calculator, use the nominal interest rate on your loan:
- ›Interest rate: pure cost of borrowing, used to calculate monthly payments
- ›APR: interest rate + fees (points, origination fees) expressed annually — always ≥ interest rate
- ›For mortgages, the difference between rate and APR is typically 0.1%–0.5%
- ›For auto loans and personal loans, fees are smaller so rate ≈ APR
The APR is most useful for comparing loans from different lenders. The interest rate drives the monthly payment calculation.
Should I choose a 15-year or 30-year mortgage?
Comparing a $300,000 mortgage:
- ›30-year at 6.8%: payment ~$1,955/mo, total interest ~$403,000
- ›15-year at 6.2%: payment ~$2,570/mo, total interest ~$162,000
- ›Difference: $615/mo more for the 15-year, saves ~$241,000 in interest
Choose 15-year if you can comfortably afford the higher payment and value being debt-free sooner. Choose 30-year for flexibility — you can always make extra payments to pay it off early.
What happens if I make bi-weekly payments instead of monthly?
The math: 52 weeks / 2 = 26 bi-weekly periods. 26 × (half payment) = 13 full payments per year. That one extra payment per year goes entirely to principal:
- ›$300,000 at 6.5%: bi-weekly saves ~$55,000 and ~4.5 years
- ›No need for a formal bi-weekly program — just make one extra principal payment each year
- ›Alternatively, divide your monthly payment by 12 and add that amount to every monthly payment
Can I use this calculator for interest-only loans?
Interest-only loans have a fundamentally different structure:
- ›During the I/O period (usually 5–10 years): payment = Balance × monthly rate
- ›Balance does not decrease during the I/O period
- ›After I/O period: remaining balance amortizes over remaining term — payment jumps sharply
- ›Total interest paid is much higher than an equivalent fully-amortizing loan
This calculator is designed for the most common loan type: fully amortizing fixed-rate mortgages, auto loans, and personal loans.
Does the calculator save my inputs?
Inputs are automatically saved to your browser's localStorage:
- ›Loan amount, annual rate, term, extra payment, and start date are all persisted
- ›Data is stored only in your browser — never sent to any server
- ›Inputs restore automatically on your next visit
- ›Click Reset All to clear both the form and the saved localStorage entry