Most general contractors should add estimating capacity when they start declining bid invitations for lack of time, not when revenue hits a particular number. Turning down work you could have won is the clearest signal that estimating has become the constraint on growth.
There is no revenue threshold that tells you to hire an estimator. Contractors ask for one constantly, and the honest answer is that the trigger is a bottleneck, not a number.
The signals that actually matter
You are declining bid invitations. Not because the work is wrong, but because there is no time to price it. This is the clearest signal there is. Every declined invitation is revenue you had access to and could not reach.
Estimating happens after the workday ends. If takeoffs are getting done at 9pm because the day was full of running jobs, you are not doing either task well. Fatigue errors in an estimate are expensive, and the jobs you are running deserve daylight attention.
Your win rate is drifting down. Rushed estimates get padded, because padding is what you do when you are not confident in the number. Padded bids lose. If your hit rate is sliding and the market has not changed, look at how much time each estimate is actually getting.
You cannot answer why you lost. A contractor with real estimating discipline can look at a lost bid and say where they were high. If every loss is a shrug, the estimates are not detailed enough to learn from.
Hire, outsource, or wait
Wait if your volume is genuinely low and the after-hours work is occasional. Not every constraint needs solving this quarter.
Outsource if your volume is seasonal, lumpy, or growing but not yet steady. Outsourced capacity flexes with the pipeline, which is the whole point when the pipeline is uneven. It also lets you find out what a dedicated estimator changes about your win rate before committing to payroll.
Hire when the volume is consistent enough to keep somebody busy year-round, and when you have the cost data and templates for a new person to actually work from. That second condition gets skipped a lot. Hiring an estimator into a company with no documented unit costs means paying somebody to rebuild your pricing history from memory, which takes months.
The mistake to avoid
Do not hire an estimator as a growth bet, hoping the volume shows up to justify them. A full-time estimator is a fixed cost, and fixed costs are exactly what you do not want carrying an uneven pipeline. Build capacity to match the work you already have access to, then scale it.
If the constraint is real but the volume is not yet steady, that gap is what outsourced estimating exists to fill.