fudge factor

noun
  1. 1

    A quantity introduced to compensate for uncertainty.

    โ€œWe don't know exactly how much the load will weigh, so we'll add in a fudge factor to make sure we don't underestimate.โ€

  2. 2

    Any padding or compensation built into a guess or estimate.

Source: https://en.wiktionary.org/wiki/fudge%20factor