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Certificate Expiry Days Calculator

Work out certificate expiry days instantly with clear inputs, formula shown and shareable results.

About Certificate Expiry Days Calculator

TLS certificate lifetimes have shortened steadily — public certificates are now capped near 398 days and ACME issuers default to 90 — which makes automated renewal essential rather than optional. Renewal should start well before expiry so there is time for retries, DNS propagation and validation failures; ACME clients conventionally renew at one third of remaining lifetime.

Formula

Expiry tracking

days remaining = validity - days elapsed; renewal due = days remaining - renewal threshold

Worked example

With the default values below, Certificate Expiry Days Calculator returns Days until expiry of 28. Change any input above and every figure here is recalculated in your browser.

Inputs used

Certificate validity periodaccepts 1–1,200 days
90 days
Days since issuanceminimum 0
62
Renew when this many days remainminimum 1
30

Results

Days until expiry
28 days
Share of validity consumed
68.9%
Days until renewal is due
-2 days
Certificate status
Renew now - inside the renewal window

Step by step

  1. 1Values used
  2. 2Expiry tracking
  3. 3Days until expiry= 28 days
  4. 4Share of validity consumed= 68.9
  5. 5Days until renewal is due= -2 days
  6. 6Certificate status= Renew now - inside the renewal window

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax or fees or charges into account.
  • Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why are certificate lifetimes getting shorter?

Short lifetimes limit the damage from an undetected key compromise and reduce reliance on revocation, which has never worked reliably at internet scale.

What renewal threshold should I set?

At least one third of the validity period, and never less than about a week. That leaves room for a failed validation to be retried without an outage.

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