{
    "name": "Churn Cohort Retention Calculator",
    "url": "https://calculators.geekmidst.com/calculators/churn-cohort-retention-calculator",
    "markdown": "https://calculators.geekmidst.com/calculators/churn-cohort-retention-calculator.md",
    "category": "Statistics & probability",
    "description": "Track one sign-up cohort over time: retention against the starting size, churn in each period, cumulative churn and the average churn rate per period.",
    "summary": "A cohort is a group that started together, such as all customers who joined in January. Following how many are still active each period gives a retention curve that new sign-ups cannot inflate.",
    "also_called": [
        "Cohort analysis calculator",
        "Retention curve 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": "cohort",
            "label": "Cohort size at the start",
            "type": "number",
            "default": "1000"
        },
        {
            "name": "active",
            "label": "Still active at the end of each period",
            "type": "textarea",
            "default": "800, 680, 612"
        }
    ],
    "outputs": [
        {
            "key": "final_retention",
            "label": "Retention at the last period",
            "format": "percent"
        },
        {
            "key": "cumulative_churn",
            "label": "Cumulative churn",
            "format": "percent"
        },
        {
            "key": "avg_period_churn",
            "label": "Average churn per period (compound)",
            "format": "percent"
        },
        {
            "key": "first_period_churn",
            "label": "First-period churn",
            "format": "percent"
        },
        {
            "key": "remaining",
            "label": "Still active",
            "format": "integer"
        },
        {
            "key": "lost",
            "label": "Lost",
            "format": "integer"
        }
    ],
    "formula": {
        "text": "Retention_t = A_t ÷ C;  Churn_t = (A_{t−1} − A_t) ÷ A_{t−1};  Average churn = 1 − (A_k ÷ C)^(1 ÷ k)",
        "variables": {
            "C": "cohort size at the start (A₀)",
            "A_t": "members still active after period t",
            "k": "number of periods"
        }
    },
    "worked_example": {
        "inputs": {
            "cohort": "1000",
            "active": "800, 680, 612"
        },
        "steps": [
            "Retention: 800, 680 and 612 of 1,000 = 80%, 68%, 61.2%.",
            "Period churn: 200 ÷ 1,000 = 20%, 120 ÷ 800 = 15%, 68 ÷ 680 = 10%.",
            "Average churn = 1 − 0.612^(1/3) ≈ 15.10% per period."
        ],
        "result": "After three periods 61.2% of the cohort remains, an average churn of about 15.1% a period."
    },
    "interpretation": "Falling period churn, as here, means the cohort is settling into a loyal core. A curve that flattens is a strong sign of product fit; one that keeps falling at the same rate is not.",
    "assumptions": [
        "The cohort is closed: reactivated and new members are excluded.",
        "Periods are equal in length."
    ],
    "limitations": [
        "Covers one cohort; compare several cohorts to see whether retention is improving.",
        "Revenue retention (expansion and downgrades) is a different measure."
    ],
    "rules": null,
    "faqs": [
        {
            "question": "Why use a compound average churn?",
            "answer": "Churn applies to a shrinking base. The compound rate is the constant churn that would leave the same number active after k periods, so it reproduces the result exactly."
        },
        {
            "question": "How is this different from a retention-rate calculation?",
            "answer": "A single-period retention rate starts from the customer count at the start and subtracts new customers. A cohort follows the same people across many periods."
        }
    ],
    "sources": [],
    "related": [
        {
            "name": "Customer Retention Rate Calculator",
            "url": "https://calculators.geekmidst.com/calculators/customer-retention-rate-calculator"
        },
        {
            "name": "Subscription Churn Calculator",
            "url": "https://calculators.geekmidst.com/calculators/subscription-churn-calculator"
        },
        {
            "name": "Time Series Growth Calculator",
            "url": "https://calculators.geekmidst.com/calculators/time-series-growth-calculator"
        }
    ],
    "disclaimer": null,
    "publisher": "GM¹X CalcVerse"
}