{
    "name": "Interest Calculator",
    "url": "https://calculators.geekmidst.com/calculators/interest-calculator",
    "markdown": "https://calculators.geekmidst.com/calculators/interest-calculator.md",
    "category": "Finance",
    "description": "See how a deposit plus monthly or yearly contributions grows with compound interest, how much tax on the interest takes, and what it is worth after inflation.",
    "summary": "Interest earns interest once it is added to the balance. This calculator adds regular deposits, deducts tax on the interest each year and shows what the final sum is worth in today’s money.",
    "also_called": [
        "Savings interest 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": "principal",
            "label": "Initial deposit",
            "type": "number",
            "default": "10000"
        },
        {
            "name": "monthly",
            "label": "Monthly contribution",
            "type": "number",
            "default": "100",
            "optional": true
        },
        {
            "name": "annual",
            "label": "Yearly contribution",
            "type": "number",
            "default": "0",
            "optional": true
        },
        {
            "name": "timing",
            "label": "Contributions made at the",
            "type": "segmented",
            "default": "end",
            "options": {
                "end": "End of period",
                "begin": "Start of period"
            }
        },
        {
            "name": "rate",
            "label": "Interest rate (per year)",
            "type": "number",
            "default": "5",
            "unit": "%"
        },
        {
            "name": "compounding",
            "label": "Compounding",
            "type": "select",
            "default": "12",
            "options": {
                "1": "Annually",
                "2": "Semi-annually",
                "4": "Quarterly",
                "12": "Monthly",
                "365": "Daily",
                "continuous": "Continuously"
            }
        },
        {
            "name": "years",
            "label": "Years",
            "type": "number",
            "default": "10",
            "unit": "years"
        },
        {
            "name": "tax",
            "label": "Tax rate on interest",
            "type": "number",
            "default": "0",
            "unit": "%",
            "optional": true
        },
        {
            "name": "inflation",
            "label": "Inflation (per year)",
            "type": "number",
            "default": "3",
            "unit": "%",
            "optional": true
        },
        {
            "name": "currency",
            "label": "Currency",
            "type": "currency",
            "default": "USD"
        }
    ],
    "outputs": [
        {
            "key": "end_balance",
            "label": "End balance",
            "format": "currency"
        },
        {
            "key": "contributions",
            "label": "Total deposited",
            "format": "currency"
        },
        {
            "key": "interest",
            "label": "Interest earned (before tax)",
            "format": "currency"
        },
        {
            "key": "tax",
            "label": "Tax on interest",
            "format": "currency"
        },
        {
            "key": "real_value",
            "label": "End balance in today’s money",
            "format": "currency"
        }
    ],
    "formula": {
        "text": "Monthly rate i = (1 + r/m)^(m/12) − 1;  each month: Balance = Balance × (1 + i) + deposits;  each year: Balance −= Tax% × interest earned that year;  Real value = Balance ÷ (1 + inflation)^years",
        "variables": {
            "r": "nominal annual interest rate",
            "m": "compounding periods per year",
            "i": "equivalent monthly rate"
        }
    },
    "worked_example": {
        "inputs": {
            "principal": "10000",
            "monthly": "0",
            "annual": "0",
            "timing": "end",
            "rate": "5",
            "compounding": "1",
            "years": "10",
            "tax": "0",
            "inflation": "0",
            "currency": "USD"
        },
        "steps": [
            "Compounded yearly at 5%, the deposit is multiplied by 1.05 each year.",
            "10,000 × 1.05^10 = 10,000 × 1.628895 = $16,288.95.",
            "Interest earned = 16,288.95 − 10,000 = $6,288.95."
        ],
        "result": "$10,000 at 5% compounded yearly grows to $16,288.95 in 10 years, earning $6,288.95 of interest."
    },
    "interpretation": "If the after-inflation value is close to what you put in, your savings are only keeping pace with prices. Tax on interest compounds too: 20% tax on a 5% rate leaves you a 4% net rate every year.",
    "assumptions": [
        "The interest rate stays the same for the whole period.",
        "Deposits earn interest from the month they are made at the equivalent monthly rate.",
        "Tax is deducted from the balance once a year on that year’s interest, at the rate you enter."
    ],
    "limitations": [
        "Tax allowances (such as tax-free interest thresholds) are not modelled; set the tax rate to 0 if your interest is tax-free.",
        "Inflation is applied as a constant yearly rate."
    ],
    "rules": null,
    "faqs": [
        {
            "question": "How is this different from the Compound Interest Calculator?",
            "answer": "This one adds yearly contributions, start-or-end timing, tax on interest and an inflation-adjusted result."
        },
        {
            "question": "Does more frequent compounding make a big difference?",
            "answer": "A little: 5% compounded daily is about 5.13% a year, against 5% compounded yearly."
        }
    ],
    "sources": [],
    "related": [
        {
            "name": "Compound Interest Calculator",
            "url": "https://calculators.geekmidst.com/calculators/compound-interest-calculator"
        },
        {
            "name": "Simple Interest Calculator",
            "url": "https://calculators.geekmidst.com/calculators/simple-interest-calculator"
        },
        {
            "name": "Inflation Calculator",
            "url": "https://calculators.geekmidst.com/calculators/inflation-calculator"
        },
        {
            "name": "Savings Goal Calculator",
            "url": "https://calculators.geekmidst.com/calculators/savings-goal-calculator"
        },
        {
            "name": "Investment Calculator",
            "url": "https://calculators.geekmidst.com/calculators/investment-calculator"
        }
    ],
    "disclaimer": "Returns are illustrations at a constant rate, not predictions or guarantees. Investments can lose value. This is not investment advice.",
    "publisher": "GM¹X CalcVerse"
}