{
    "name": "TLS Certificate Expiry Calculator",
    "url": "https://calculators.geekmidst.com/calculators/tls-certificate-expiry-calculator",
    "markdown": "https://calculators.geekmidst.com/calculators/tls-certificate-expiry-calculator.md",
    "category": "IT, networking & security",
    "description": "Work out when a TLS/SSL certificate expires from its issue date and validity, how many days are left, and the date to renew with your chosen lead time.",
    "summary": "A certificate stops being trusted after its “not after” date. Enter the issue date and lifetime (or expiry date) to see the days left and the latest comfortable renewal date.",
    "also_called": [
        "SSL certificate expiry calculator",
        "Certificate renewal 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": "issued",
            "label": "Issued on (not before)",
            "type": "date",
            "default": "2026-10-01"
        },
        {
            "name": "mode",
            "label": "Lifetime given as",
            "type": "segmented",
            "default": "days",
            "options": {
                "days": "Validity in days",
                "date": "Expiry date"
            }
        },
        {
            "name": "validity_days",
            "label": "Validity",
            "type": "number",
            "default": "90",
            "unit": "days",
            "shown_when": {
                "mode": "days"
            }
        },
        {
            "name": "expires",
            "label": "Expires on (not after)",
            "type": "date",
            "default": "2026-12-30",
            "shown_when": {
                "mode": "date"
            }
        },
        {
            "name": "asof",
            "label": "Check on",
            "type": "date",
            "default": "",
            "optional": true
        },
        {
            "name": "renew_before",
            "label": "Renew this many days before expiry",
            "type": "number",
            "default": "30",
            "unit": "days"
        }
    ],
    "outputs": [
        {
            "key": "days_left",
            "label": "Days until expiry",
            "format": "integer"
        },
        {
            "key": "expiry_date",
            "label": "Expiry date",
            "format": "text"
        },
        {
            "key": "renew_on",
            "label": "Renew on or before",
            "format": "text"
        },
        {
            "key": "status",
            "label": "Status",
            "format": "text"
        },
        {
            "key": "lifetime_days",
            "label": "Certificate lifetime",
            "format": "integer"
        },
        {
            "key": "lifetime_used",
            "label": "Lifetime used",
            "format": "percent"
        }
    ],
    "formula": {
        "text": "Expiry = Issue date + Validity days;  Days left = Expiry − Check date;  Renew on = Expiry − Lead days",
        "variables": {
            "Validity days": "certificate lifetime",
            "Lead days": "how early you want to renew"
        }
    },
    "worked_example": {
        "inputs": {
            "issued": "2026-10-01",
            "mode": "days",
            "validity_days": "90",
            "expires": "2026-12-30",
            "asof": "2026-10-29",
            "renew_before": "30"
        },
        "steps": [
            "1 October + 90 days: +30 → 31 October, +30 → 30 November, +30 → 30 December 2026.",
            "From 29 October to 30 December: 2 + 30 + 30 = 62 days.",
            "Renewing 30 days ahead means by 30 November 2026."
        ],
        "result": "A 90-day certificate issued on 1 October 2026 expires on 30 December 2026: 62 days left on 29 October, renew by 30 November."
    },
    "interpretation": "Automate renewal where you can (ACME clients such as certbot) and monitor the expiry date independently, since a missed renewal takes the site offline for visitors with a browser warning.",
    "assumptions": [
        "Whole calendar days in UTC; the exact expiry time of day is in the certificate’s notAfter field."
    ],
    "limitations": [
        "Maximum lifetimes for publicly trusted certificates are set by the CA/Browser Forum and are being reduced in stages; check your CA’s current limit."
    ],
    "rules": null,
    "faqs": [
        {
            "question": "How long can a public TLS certificate be valid?",
            "answer": "The CA/Browser Forum’s ballot SC-081v3, passed in April 2025, reduces the maximum in stages from 398 days, starting in March 2026, to 47 days by March 2029."
        },
        {
            "question": "How do I find my certificate’s dates?",
            "answer": "Click the padlock in your browser and view the certificate, or run openssl x509 -noout -dates on the certificate file."
        }
    ],
    "sources": [
        {
            "title": "CA/Browser Forum: Ballot SC-081v3, reducing validity and data reuse periods",
            "url": "https://cabforum.org/2025/04/11/ballot-sc081v3-introduce-schedule-of-reducing-validity-and-data-reuse-periods/"
        }
    ],
    "related": [
        {
            "name": "Date Difference Calculator",
            "url": "https://calculators.geekmidst.com/calculators/date-difference-calculator"
        },
        {
            "name": "DNS TTL Cache Window Calculator",
            "url": "https://calculators.geekmidst.com/calculators/dns-ttl-cache-window-calculator"
        },
        {
            "name": "Password Entropy Calculator",
            "url": "https://calculators.geekmidst.com/calculators/password-entropy-calculator"
        }
    ],
    "disclaimer": null,
    "publisher": "GM¹X CalcVerse"
}