555 Timer Calculator

Design or analyze the classic NE555 timer in astable (free-running oscillator) or monostable (one-shot) mode. Enter the timing resistors and capacitor to get frequency, period, high/low times and duty cycle, or flip to design mode and enter a target frequency to solve for the capacitor. The standard formulas use the internal resistor-divider thresholds at 1/3 and 2/3 of VCC. Useful for blinking LEDs, clock generation, debounce and time-delay circuits. Pure arithmetic — the 555's real accuracy depends on the chip variant, supply voltage, capacitor tolerance and temperature, so use 1% resistors and a low-leakage cap for precision timing. Everything runs locally in your browser.