Clock Skew Budget Calculator

Work out clock skew budget instantly with clear inputs, formula shown and shareable results.

About Clock Skew Budget Calculator

Clock uncertainty — skew plus jitter — comes directly off the cycle time available to logic. Skew targets are typically 2-5% of the period, so at 500 MHz that is 40-100 ps, and every picosecond of uncertainty is a picosecond of logic depth lost.

Formula

Clock budget

uncertainty = skew + jitter; usable cycle = period - uncertainty

Worked example

With the default values below, Clock Skew Budget Calculator returns Skew budget of 60.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Clock period: 2 ns
Clock insertion delay: 0.45 ns
Skew target: 3 %
Clock jitter: 0.03 ns

Results

Skew budget: 60.00 ps
Total clock uncertainty: 90.00 ps
Cycle time available to logic: 1.9100 ns
Clocking overhead: 4.50% %

Step by step

1Values used
2Clock budget
3Skew budget= 60.00 ps
4Total clock uncertainty= 90.00 ps
5Cycle time available to logic= 1.9100 ns
6Clocking overhead= 4.50 %

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 not aim for zero skew?

Perfectly balanced clock trees cost enormous buffer count and power. A small deliberate skew can even help by borrowing time between pipeline stages.

Does skew help hold timing?

No, it hurts both. Skew subtracts from setup slack on one path and from hold slack on another, which is why balanced trees matter for both checks.