How accurate is the timing?

It uses performance.now for sub-millisecond accuracy. Browsers throttle background tabs, so a backgrounded stopwatch may drift a few hundred milliseconds over long intervals.

What's the difference between lap and split?

A lap is the time since the last lap button press. A split is the cumulative time at that lap. Both are recorded so you can see per-lap performance and overall elapsed time.

Will the timer sound if the tab is in the background?

Yes if you grant notification permission, or if the tab is loaded; browsers may delay audio in fully throttled background tabs. Use a desktop notification for reliability.

Is timing data uploaded?

No. Times, laps, and settings stay in your browser's local storage.

rAF · lap timer · countdown · live

Browser stopwatch & countdown timer

requestAnimationFrame-driven stopwatch with laps, or a target-seconds countdown. Works offline — no permission required.

Stopwatch & Timer

Mode

stopwatch

selected

Display

00:00:00.00

live

Laps

captured

Status

idle

state

input · controls

Counts up forever. Hit Lap to capture a split.

output · display

00:00:00.00

Quick Start

How the timer ticks

requestAnimationFrame fires roughly 60 times per second. We capture performance.now() at start and on each frame compute elapsed time from there — accurate even when tabs throttle.

01
Pick mode
Stopwatch counts up. Timer counts down from a target.
Parsing accepts ISO 8601, RFC 3339, RFC 2822, and Unix epoch seconds/milliseconds. The Date constructor handles the rest with browser-engine consistency.
modeISO 8601RFC 3339epochlive
mode · timestamppick · ISO
```
stopwatch
```
loaded · ISO 8601zone · ready
02
Start the clock
performance.now() is the anchor.
All math runs in UTC internally to avoid DST landmines; presentation converts back to the user’s zone via Intl.DateTimeFormat.
startUTC mathIntlDST-safelive
▶ · optionsnow · live
```
▶ running
```
options applied · UTCDST-safe
03
Capture laps
Click Lap to save a split. Latest first.
Output respects the chosen timezone offset (Z vs +05:30) and pads digits per ISO conventions so sorts stay chronological.
lapoffsetzone-awaresortablepadded
⚑ · computedsplit · ready
```
L3: 12.45s
```
computed · instantsortable
04
Reset state
Reset returns everything to zero and clears laps.
Copy writes via the Async Clipboard API; nothing pings a time server — the browser’s clock is the only oracle.
resetclipboardno oracledeterministicclient-side
↺ · copiedready · done
```
↺ ready
```
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 use a browser clock

Workouts, cooking, focus.

Workouts

Lap a circuit without leaving the browser. 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

Cooking

Countdown for the next stir. 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

Public speaking

Lap each section while you rehearse. 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

Dev demos

Time how long a UX flow takes for QA notes. 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

Meetings

Stand-up timer per person. 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

Quizzes

Per-question countdown. 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

Does it work in background tabs?

Browser throttles rAF in background tabs, but the time-base is performance.now() so when you return the display catches up instantly.

Sub-second precision?

Centiseconds shown. Underlying clock is sub-millisecond.

Audio alarm?

No alarm — just the visual red state. Add notifications via Pomodoro Timer.

How long can it run?

Hours fine. After many days the centi-counter may overflow on slower devices.

Is anything sent to a server?

No. All timing is local.

Suggest a tool

Something missing?

Tell us what you need. We ship the top requests every two weeks.

47 in queue·8 shipped this month

Request queued. Thanks!