Work out timer prescaler value instantly with clear inputs, formula shown and shareable results.
The prescaler must be large enough that the tick count fits in the timer, so the minimum is clock times period divided by 2^bits. Choosing the next available power of two and rounding the reload value gives the achievable period, and the rounding error is what shows up as timing drift.
Prescaler
ticks = f x period; prescaler >= ticks / 2^bits; reload = round(ticks / prescaler)
It gives the finest resolution, so the rounded reload value lands closer to the exact period and the timing error is smaller.
Choose a clock frequency that divides evenly — this is why 32.768 kHz crystals and 12/24/48 MHz clocks are so common in timing-critical designs.