Every job must carry a share of overhead, or the company loses money even on jobs that look profitable.
Example: an estimator's salary, the office lease, accounting software and company vehicles are overhead for a specialty contractor.
Work out your overhead from your own books for the past year. Compare it to your direct costs or revenue to get a recovery rate. Apply that rate in every estimate, before profit. Review it each year, because it changes as the company grows or shrinks.