millis() Overflow Calculator
When any tick counter wraps and whether your interval survives it — with the unsigned-subtraction idiom explained.
millis() wraps at 49.7 days and micros() at 71.6 MINUTES — long-uptime devices hit both. The bug is never the wrap itself but the comparison style: `now >= start + interval` breaks at wrap, `(now − start) >= interval` with unsigned types does not. Never compare timestamps with signed ints, and never measure an interval longer than half the wrap span.
millis() Overflow Calculator computes when tick counters wrap and whether your interval arithmetic survives it — free, instant and private in your browser. Firmware developers whose devices mysteriously misbehave after weeks of uptime use it to skip the datasheet algebra: type your numbers, read the answer with the substituted formula shown step by step, and share an exact permalink of the calculation.
About millis() Overflow Calculator
millis() Overflow Calculator computes when tick counters wrap and whether your interval arithmetic survives it using the standard engineering relation: wrap = 2ⁿ·tick; unsigned (now − start) is wrap-proof for gaps < half the span. Worked live: millis() wraps at 49.7 days, micros() at just 71.6 minutes — long-uptime devices meet both. The result recalculates on every keystroke, the worked-example panel shows your numbers substituted into the formula, and the Copy permalink button encodes the inputs in the URL so a colleague opens exactly your calculation. Everything runs client-side — nothing you type leaves your device.
How to use millis() Overflow Calculator
- 1Enter your values — the tool starts with realistic defaults for this exact use case, so the worked example is meaningful immediately.
- 2Read the live result and the worked-example panel, which substitutes your numbers into the formula step by step.
- 3Adjust any input to compare scenarios, then use Copy result or Copy permalink to share the calculation.
Why use millis() Overflow Calculator?
- ✓Implements the real formula — wrap = 2ⁿ·tick — with the substitution shown, not a black box
- ✓Built for firmware developers whose devices mysteriously misbehave after weeks of uptime
- ✓Copy result and permalink buttons — share the exact calculation in a README, forum answer or design review
- ✓100% free, no sign-up, runs entirely in your browser (works offline once loaded)
Frequently asked questions
How do you calculate millis() overflow?+
When tick counters wrap and whether your interval arithmetic survives it follows wrap = 2ⁿ·tick; unsigned (now − start) is wrap-proof for gaps < half the span. For example, millis() wraps at 49.7 days, micros() at just 71.6 minutes — long-uptime devices meet both. The calculator applies the same relation and shows the substituted arithmetic so you can verify every step.
What's the correct wrap-safe timing idiom?+
if ((unsigned long)(millis() − start) >= interval). Unsigned subtraction is modular, so one wrap between start and now cancels out. The broken version — now >= start + interval — fails spectacularly when start + interval overflows first.
Why must the interval stay under half the counter span?+
Modular arithmetic can't distinguish 'just elapsed' from 'elapsed plus one full wrap'. Below half the span the interpretation is unambiguous; beyond it your 50-day timer on millis() needs a wider counter — count days in software or use 64-bit tick APIs.
Is the millis() Overflow Calculator free and private?+
Yes — completely free with no sign-up or usage limits, and it runs entirely in your browser: the values you enter are never uploaded or stored on a server.
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