Certificate Expiration & Validity Calculator
Certificate Expiration & Validity Calculator: Parses ASN.1 NotBefore and NotAfter validity timestamps, compares with current system clock.
About this certificate expiration & validity calculator
Parses ASN.1 NotBefore and NotAfter validity timestamps, compares with current system clock Runs entirely in-memory using Web Crypto primitives to keep sensitive tokens, certificates, and cryptographic keys secure from third-party interception.
Encoding & cryptographic principles
Reads one or more PEM certificates, extracts their not-before and not-after times, and compares each with the current browser clock. It reports dates and remaining days; it does not validate trust, hostname, or revocation.
Worked verification example
Scenario: Parse the supplied CZOA sample PEM in the bundled @peculiar/x509 library.
Sample input:
Processing: Decode its PEM body, read notBefore and notAfter, then compare those dates with the current browser clock.
Illustrative output:
Security parameters & input constraints
This checks each parsed certificate's notBefore/notAfter against the local clock only. It does not build or validate a trust chain, check signatures, hostnames, revocation, CT logs, or server deployment; an untrusted certificate can still appear 'valid' by date. The status and remaining days change with time and clock accuracy.
Cryptographic digests, encoded strings, and signatures generated by Certificate Expiration & Validity Calculator should be verified against target authentication systems before production use.
Client-side Web Crypto boundary
Key derivation, hashing, and encoding in Certificate Expiration & Validity Calculator execute in local memory using Web Crypto APIs without remote socket transmission.
Cryptographic specifications & RFC standards
Technical specifications and cryptographic RFC standards governing algorithms and key representations:
Certificate Expiration & Validity Calculator verification · Audit standards
How to use it
- Paste one or more complete PEM CERTIFICATE blocks into the input box.
- Run locally to parse each certificate's subject and validity dates and compare them with the current browser clock.
- Read or copy the JSON array of subject, notBefore, notAfter, status, and daysRemaining for each block.
Frequently asked questions
What certificate input does the calculator parse?+
It finds complete PEM certificate blocks, Base64-decodes each body, and parses the bytes with the bundled @peculiar/x509 library in the browser.
What does each result contain?+
For each parsable certificate it returns subject, ISO notBefore, ISO notAfter, status from the current browser clock, and daysRemaining rounded upward from the remaining milliseconds.
What does the included PEM example show?+
The included CZOA sample PEM has subject CN=CZOA sample, notBefore 2026-09-05T13:39:43.000Z and notAfter 2027-09-05T13:39:43.000Z. Status and remaining days depend on the current clock; this does not test a remote TLS connection.
What is not a validity decision?+
The page does not fetch a server certificate, build a chain, check revocation, hostname, key usage, trust store, clock accuracy, or whether a deployment actually presents the supplied PEM.