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SSL / TLS Certificate Expiry Calculator

Date math on validity fields you enter.

Page updated 2026-09-14.

SSL / TLS Certificate Expiry Calculator visual
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Calculator

Certificate notAfter.

Certificate notBefore.

Calculated Results

Days remaining

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Valid window days

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Days remaining, computed from two dates

A certificate valid from 2025-09-03 to 2026-12-31 has a total valid window of 484 days. From today's date, 106 days remain before expiry, and the certificate's current status shows as valid.

A 484-day validity window is longer than the 397-day maximum that public CAs have enforced for publicly-trusted TLS certificates since 2020 -- if this were a real publicly-trusted certificate rather than an example, a window this long would indicate either an internal/private CA or an error in the dates.

Days-remaining is a simple date subtraction from today, which means this number decreases by exactly 1 every day that passes -- there's no grace period or rounding; a certificate reading '1 day remaining' today reads '0' or shows as expired tomorrow.

What this doesn't check

Date math only. This does not parse PEM or contact a host. This calculator only performs date arithmetic on the not-before and not-after dates you type in -- it doesn't parse an actual PEM certificate file, verify a certificate chain, or connect to a live host to check what certificate is actually being served right now.

A certificate can be within its valid date window (as this one is) and still fail in practice for other reasons: hostname mismatch, an untrusted or incomplete certificate chain, or revocation -- none of which a pure expiry-date calculation detects.

For monitoring real production certificates, an automated expiry-alerting system that actually queries the live certificate is more reliable than manually re-checking dates here, since it catches unexpected renewal failures or certificate changes automatically.

Related certificate and DNS checks

If the concern is whether a certificate's full chain (leaf, intermediate, root) is served in the correct order, the SSL Certificate Chain Order Checker addresses that separately.

For the DNS record that a domain's certificate validation or routing might depend on, the DNS Record Inspector & Parser parses individual DNS lines.

Frequently Asked Questions (FAQ)

How is the 484-day valid window calculated?

It's the difference between not-before (2025-09-03) and not-after (2026-12-31) dates, expressed in days -- the full lifespan of the certificate's validity period.

How are the 106 days remaining calculated?

It's the difference between today's date and the not-after (expiry) date, in days. This number changes daily and reflects however much time is actually left as of when you run the calculator.

Why would a 484-day validity window be unusual for a real certificate?

Public certificate authorities have capped publicly-trusted TLS certificate validity at 397 days since September 2020. A window longer than that typically indicates a private/internal CA (common for internal tools or intranets) rather than a publicly-trusted certificate.

Does 'valid' status mean the certificate will actually work in a browser?

Date math only. This does not parse PEM or contact a host. Not necessarily. 'Valid' here only means today's date falls within the not-before/not-after window. A real certificate can still fail due to hostname mismatch, chain issues, or revocation, none of which this date-only calculation checks.

Can I paste a real certificate file into this tool to check its dates?

No, this calculator takes plain not-before and not-after dates as text input -- it doesn't parse a PEM-encoded certificate file. You'd need to extract those two dates from the certificate yourself (or with a separate certificate-parsing tool) before entering them here.

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