A good estimate should include a contingency allowance primarily to:

解析

A contingency is money set aside inside the estimate to absorb unforeseen site conditions and the normal imprecision of estimating, so a small surprise does not have to become a claim. It is not profit: spending it leaves the margin intact, while treating it as profit means pricing the risk twice. Retention is the owner's money withheld from payments - five percent on public works under Public Contract Code section 7201, and capped at five percent on private contracts entered into on or after 1 January 2026 by Civil Code section 8811 - so it is money not yet received rather than a cost to fund. And owner-requested changes are paid through change orders at agreed prices, which is why they sit outside the contingency.