Most solo bidders don't think of themselves as guessing. They think of themselves as experienced — which is true, and also not quite the same thing. Experience tells you roughly where a number should land. It doesn't verify that the number in front of you actually got there the right way.
Here's the checklist a solid estimator runs, almost unconsciously, before a bid goes out. Doing it consciously — even just once, on your next bid — will show you where your own process has gaps.
1. Does every line item trace back to a real quantity?
Not "about how much drywall," but a measured square footage. Not "roughly this many linear feet," but a number pulled from the plan. If you can't point to where a number came from, it's a guess, however educated.
2. Is the waste factor specific to this job?
Pull up your last bid. Is the waste percentage identical to the one before it? If so, ask whether that's because the jobs were genuinely similar, or because the number didn't get revisited.
3. What's explicitly excluded — and does the client know it?
Say it out loud, or better, write it down. If you can't finish the sentence "this bid does not include ___," you probably haven't thought hard enough about the edges of the scope.
4. Where's the labor rate coming from?
Current market conditions, or a number that's been sitting in your head since last year? Labor costs move. If your rate hasn't moved with them, your margin is quietly shrinking even when your bid looks the same as always.
5. Would this bid survive someone else checking it?
This is the real test. If a second set of eyes went through it line by line, would every number hold up, or are there two or three places you'd rather they didn't look too closely?
Run it before you send
Run through these five questions on your next bid before you send it. Most estimating mistakes aren't from a lack of skill — they're from skipping one of these five under time pressure. Building them into your process, every time, is the difference between bidding from experience and bidding from a checklist that happens to include experience as one input.