Which API powers the output?

Intl.RelativeTimeFormat, a standard browser API shipped in all modern browsers. It uses the CLDR locale database to produce natural phrasing in each language.

What's the difference between numeric: 'always' and 'auto'?

'always' forces phrasing like "1 day ago". 'auto' lets the formatter pick natural alternatives like "yesterday" or "tomorrow" when they fit.

Can it format both past and future?

Yes. Pass a negative duration for the past, positive for the future. The formatter picks the right phrasing automatically ("3 hours ago" vs "in 3 hours").

humanize · 5 min ago · in 3 days · live

Humanize a date as relative time

Q: Is anything sent to a server?

No. Formatting runs entirely in your browser via the Intl API.

"5 minutes ago" / "in 3 days" — the same style every social network uses. Largest fitting unit wins, sign tells past vs future.

Quick Start

How humanizing works

We compute the absolute delta in seconds, then pick the largest unit whose threshold isn't exceeded — second, minute, hour, day, week, month, year. Round and add ago / in.

01
Paste a date
ISO, RFC 2822, or any string Date() can parse.
Parsing accepts ISO 8601, RFC 3339, RFC 2822, and Unix epoch seconds/milliseconds. The Date constructor handles the rest with browser-engine consistency.
inputISO 8601RFC 3339epochlive
in · timestampany · ISO
```
2024-01-01
```
loaded · ISO 8601zone · ready
02
Diff vs now
We sample Date.now() every second so the phrase stays current.
All math runs in UTC internally to avoid DST landmines; presentation converts back to the user’s zone via Intl.DateTimeFormat.
liveUTC mathIntlDST-safe
Δ · optionslive · live
```
now - target
```
options applied · UTCDST-safe
03
Pick largest unit
If under 60s we say seconds; under 60m, minutes; etc.
Output respects the chosen timezone offset (Z vs +05:30) and pads digits per ISO conventions so sorts stay chronological.
pickoffsetzone-awaresortablepadded
unit · computedbest · ready
```
< 1h → minutes
```
computed · instantsortable
04
Add direction
Past dates get "ago", future dates get "in".
Copy writes via the Async Clipboard API; nothing pings a time server — the browser’s clock is the only oracle.
textclipboardno oracledeterministicclient-side
ago · copiedin · done
```
✓ Copied
```
shipped · ready to shipsuccess

Pro tips

Time math without DST landmines

Always store UTC

Convert to local for display only. UTC storage avoids DST jumps and timezone drift in databases.

Watch leap seconds

POSIX time doesn’t count leap seconds; some systems do. Don’t use timestamps for sub-second precision across boundaries.

Prefer Temporal eventually

The Date API has many quirks. Temporal is shipping in modern engines and handles zones correctly.

Cron is timezone-tricky

Cron expressions run in the daemon’s local zone unless told otherwise. Pin a TZ explicitly for predictable runs.

ISO 8601 sorts naturally

YYYY-MM-DDTHH:mm:ss sorts correctly as a string. Don’t use US-style MM/DD/YYYY for anything machine-readable.

Beware Y2K38

Signed 32-bit Unix timestamps overflow in 2038. Use 64-bit storage end-to-end for long-lived systems.

Use Cases

When to humanize a date

UI labels, copy generation, notifications.

Activity feeds

"Posted 5 minutes ago" instead of a raw timestamp. Math runs in UTC under the hood to dodge DST jumps — local time is only for display. That means scheduling logic and date diffs survive March / November fall-back without the classic off-by-one-hour bug.

DST-safe

Issue trackers

"Updated 2 days ago" for last activity columns. Browser clock is the only source — no external time server, no privacy leak, no rate limit. Pair with NTP-synced server time for high-accuracy use cases, but for human-scale work the browser clock is plenty.

UTC-correct

Notifications

"in 1 hour" for upcoming reminders. ISO 8601 output sorts naturally as strings, perfect for filenames (report-2026-01-15.pdf) and log lines that need chronological ordering without parsing. Drop into S3 keys for free time-bucketing.

ISO-sortable

Mock data

Generate realistic relative labels for prototype screens. Pairs cleanly with cron, scheduled tasks, and timestamped log analysis. The tool's output drops directly into APScheduler, Linux cron, or GitHub Actions schedule expressions without re-formatting.

spec-grade

Status pages

"Resolved 3 hours ago" tells users what they need. Output respects the chosen timezone offset (Z vs +05:30) so REST APIs and database TIMESTAMP WITH TIME ZONE columns round-trip cleanly. No ambiguity between "noon UTC" and "noon local".

zone-aware

Tooltip detail

Show humanized text with absolute date on hover. Confirms the difference between epoch seconds (10 digits) and milliseconds (13 digits) before you commit code that mis-multiplies by 1000 — a classic bug in cross-language time handling.

epoch-accurate

FAQ

Frequently asked questions

Is this Intl.RelativeTimeFormat?

Same idea, simpler logic — pure JS for predictable English output. Use Intl.RelativeTimeFormat if you need i18n.

How are months / years computed?

30-day month, 365-day year — averages. Good enough for UI labels; not for precise math.

Why round?

Humans say 'in 3 days' not 'in 2.97 days'. Rounding to nearest integer is the social-network default.

Singular vs plural?

1 minute, 2 minutes — the s is appended only for non-1 values.

Is anything sent to a server?

No — humanizing runs locally in your browser tab.

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