วิธีการคำนวณ SSL Certificate Expiry

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The SSL Certificate Expiry Calculator computes days remaining until an SSL/TLS certificate expires, identifies urgent renewal needs, and calculates renewal reminder dates based on your preferred lead time (default 30 days). SSL/TLS certificates secure HTTPS connections by encrypting data and verifying server identity. Expired certificates cause browser security warnings, broken HTTPS, and erode user trust — making expiry tracking essential for any site or API.

สูตร

exp

Expiry Date (date) — Certificate notAfter timestamp

iss

Issued Date (date) — Certificate notBefore timestamp

คำแนะนำทีละขั้นตอน

1. 1Enter the certificate expiration date (visible in browser by clicking the padlock icon)
2. 2Optionally enter the issued date for total validity period and percent-of-life-used calculation
3. 3Set your reminder lead time in days (30 default; some teams use 14 or 60)
4. 4Calculator computes days until expiry and renewal reminder date
5. 5Status: HEALTHY (>30 days), RENEW SOON (within reminder threshold), URGENT (<7 days), EXPIRED (negative days)
6. 6Pull total certificate validity from issued + expiry dates if both provided
7. 7Visual bar compares days left to your reminder threshold

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ข้อผิดพลาดที่ควรหลีกเลี่ยง

• ✕Manually tracking expiration without automated alerts — most outages from expired certs happen because nobody was watching
• ✕Ignoring intermediate certificates — full chain must be valid, not just the leaf cert
• ✕Not testing renewal in advance — Let's Encrypt renewals can fail silently due to ACME challenge issues
• ✕Forgetting wildcard cert renewals affect all subdomains simultaneously

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