Setup And Hold Slack Calculator

Work out setup and hold slack instantly with clear inputs, formula shown and shareable results.

About Setup And Hold Slack Calculator

Setup slack is clock period minus data path delay minus setup time minus skew: it must be positive or the flip-flop samples before the data arrives. Hold slack is the opposite constraint — the data must not arrive too early — and it cannot be fixed by slowing the clock.

Formula

Timing slack

setup slack = T - t_data - t_setup - skew; hold slack = t_data - t_hold - skew

Worked example

With the default values below, Setup And Hold Slack Calculator returns Setup slack of 0.2000. Change any input above and every figure here is recalculated in your browser.

Inputs used

Clock period: 1.25 ns
Data path delay: 0.92 ns
Flip-flop setup time: 0.08 ns
Clock skew: 0.05 ns

Results

Setup slack: 0.2000 ns
Hold slack: 0.8400 ns
Maximum frequency: 0.95 GHz
Timing verdict: Timing met

Step by step

1Values used
2Timing slack
3Setup slack= 0.2000 ns
4Hold slack= 0.8400 ns
5Maximum frequency= 0.95 GHz
6Timing verdict= Timing met

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax or fees or charges into account.
Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why can hold violations not be fixed by slowing the clock?

Hold checks compare paths within the same clock edge, so the period does not appear in the equation. The only fix is adding delay to the data path.

What does negative setup slack mean?

The path cannot run at that frequency. Options are logic restructuring, gate upsizing, pipelining or lowering the clock frequency.