{
    "name": "Mortgage Amortization Calculator",
    "url": "https://calculators.geekmidst.com/calculators/mortgage-amortization-calculator",
    "markdown": "https://calculators.geekmidst.com/calculators/mortgage-amortization-calculator.md",
    "category": "Finance",
    "description": "See a year-by-year mortgage amortization schedule and how extra monthly or one-off payments cut the interest you pay and the time until the loan is gone.",
    "summary": "Every extra payment goes straight to principal, so it removes all the future interest on that amount. This schedule compares your mortgage with and without extra payments.",
    "also_called": [
        "Mortgage payoff calculator",
        "Extra payment calculator"
    ],
    "applies_to": "Worldwide",
    "last_updated": "2026-10-29",
    "computation": "Results are computed in the visitor’s browser on the HTML page. This API describes the calculator; it does not compute results.",
    "inputs": [
        {
            "name": "loan",
            "label": "Mortgage amount",
            "type": "number",
            "default": "300000"
        },
        {
            "name": "rate",
            "label": "Interest rate (per year)",
            "type": "number",
            "default": "6.5",
            "unit": "%"
        },
        {
            "name": "years",
            "label": "Term",
            "type": "number",
            "default": "30",
            "unit": "years"
        },
        {
            "name": "extra",
            "label": "Extra payment every month",
            "type": "number",
            "default": "200",
            "optional": true
        },
        {
            "name": "lump",
            "label": "One-off extra payment",
            "type": "number",
            "default": "0",
            "optional": true
        },
        {
            "name": "lump_month",
            "label": "Paid in month number",
            "type": "number",
            "default": "12",
            "optional": true
        },
        {
            "name": "currency",
            "label": "Currency",
            "type": "currency",
            "default": "USD"
        }
    ],
    "outputs": [
        {
            "key": "interest_saved",
            "label": "Interest saved",
            "format": "currency"
        },
        {
            "key": "payment",
            "label": "Regular monthly payment",
            "format": "currency"
        },
        {
            "key": "total_interest",
            "label": "Total interest with extra payments",
            "format": "currency"
        },
        {
            "key": "payoff_months",
            "label": "Months to pay off",
            "format": "integer"
        },
        {
            "key": "months_saved",
            "label": "Months saved",
            "format": "integer"
        },
        {
            "key": "total_paid",
            "label": "Total paid",
            "format": "currency"
        }
    ],
    "formula": {
        "text": "Payment A = L × r × (1 + r)ⁿ ÷ ((1 + r)ⁿ − 1). Each month: interest = balance × r; balance = balance + interest − A − extra.",
        "variables": {
            "L": "mortgage amount",
            "r": "annual rate ÷ 12 ÷ 100",
            "n": "term in months",
            "extra": "extra principal paid that month"
        }
    },
    "worked_example": {
        "inputs": {
            "loan": "300000",
            "rate": "6.5",
            "years": "30",
            "extra": "200",
            "lump": "0",
            "lump_month": "12",
            "currency": "USD"
        },
        "steps": [
            "Regular payment on $300,000 at 6.5% over 360 months = $1,896.20; interest over the full term = $382,633.47.",
            "Paying $200 extra each month, the balance reaches zero after 277 payments.",
            "Interest falls to $279,184.67, a saving of $103,448.79, and the loan ends 83 months (almost 7 years) early."
        ],
        "result": "An extra $200 a month on a $300,000, 6.5% mortgage saves about $103,000 of interest and clears it nearly 7 years early."
    },
    "interpretation": "Extra payments made early in the loan save the most, because they remove interest for the longest time. Check that your lender applies extra payments to principal and does not charge prepayment penalties.",
    "assumptions": [
        "Fixed rate; the regular payment stays the same and extra payments shorten the term.",
        "Extra payments are applied to principal in the month they are made."
    ],
    "limitations": [
        "Prepayment limits or penalties, taxes and insurance are not modelled."
    ],
    "rules": null,
    "faqs": [
        {
            "question": "Is it better to pay extra or invest?",
            "answer": "Paying extra earns a guaranteed return equal to your mortgage rate. Investing may earn more or less; compare after tax and risk."
        },
        {
            "question": "How is this different from the loan amortization calculator?",
            "answer": "This page models extra monthly and one-off payments and summarises the schedule by year; the loan amortization calculator shows a plain month-by-month schedule."
        }
    ],
    "sources": [],
    "related": [
        {
            "name": "Loan Amortization Calculator",
            "url": "https://calculators.geekmidst.com/calculators/loan-amortization-calculator"
        },
        {
            "name": "Mortgage Calculator",
            "url": "https://calculators.geekmidst.com/calculators/mortgage-calculator"
        },
        {
            "name": "UK Mortgage Calculator",
            "url": "https://calculators.geekmidst.com/calculators/mortgage-calculator-uk"
        },
        {
            "name": "Canadian Mortgage Calculator",
            "url": "https://calculators.geekmidst.com/calculators/canadian-mortgage-calculator"
        }
    ],
    "disclaimer": "This calculator gives estimates for planning. It is not financial advice, and lenders’ actual terms, fees and rounding may differ.",
    "publisher": "GM¹X CalcVerse"
}