Cache TTL Calculator

A cache TTL (time-to-live) is how long a stored response — a browser cache entry, a CDN edge cache, a Redis key — is considered "fresh" before it must be re-fetched or re-validated against the origin. On the web, the most common way to express a TTL is the HTTP Cache-Control: max-age=<seconds> response header, where the value is always in seconds, not minutes or hours. That mismatch — thinking in hours or days but having to type seconds — is where mistakes creep in (a typo turns "1 day" into 864 seconds instead of 86400).

This calculator removes the arithmetic. Enter a TTL value and pick its unit (seconds, minutes, hours, days or weeks), and it instantly converts the value to total seconds, spells out a human-readable duration, and writes the matching Cache-Control: max-age= header string you can paste straight into server config, a CDN rule, or application code.

How to use it

1. Enter the TTL Value — any non-negative number, including decimals (e.g. 1.5).
2. Choose the Unit — Seconds, Minutes, Hours, Days or Weeks.
3. Read the result table:
   • Total Seconds — the raw number max-age expects.
   • Human-Readable Duration — the same value broken into weeks, days, hours, minutes and seconds (e.g. "1 day, 12 hours").
   • Cache-Control Header — the ready-to-use header string (Cache-Control: max-age=7200).
   • Expires Header (relative) — a reminder that the older Expires header (an absolute date) is equivalent to "the current time plus this many seconds," for systems that still emit Expires instead of max-age.

The result updates automatically as you type — there's no button to click.

FAQ

Why seconds specifically? max-age (and its shared-cache sibling s-maxage) are defined in the HTTP spec as an integer number of seconds. This tool rounds fractional results (e.g. 1.5 minutes) to the nearest whole second, since max-age doesn't support fractions.

What does max-age=0 mean? Zero seconds means the cached response is immediately stale — clients should revalidate with the origin before reusing it. It's different from no-store, which forbids storing the response at all; max-age=0 still allows caching, just with mandatory revalidation.

Is there a maximum useful TTL? Practically, values much beyond a year (31536000 seconds) rarely add value — most browsers and CDNs cap effective caching well below that, and very long TTLs make it hard to roll out changes without cache-busting (e.g. versioned filenames). Days-to-weeks is typical for static assets; seconds-to-minutes is typical for dynamic API responses.

What about s-maxage, stale-while-revalidate, or other Cache-Control directives? This tool focuses on converting a single TTL into max-age. Any of the directives above use the same "seconds" unit, so the Total Seconds value here plugs directly into s-maxage=<seconds>, stale-while-revalidate=<seconds>, etc. if you're hand-assembling a more complex header.

Privacy

Everything runs locally in your browser — the TTL value you enter is never sent to a server.