What software or service do startups use for cost projections?

Matt: do you mean budget/planning, BOM analysis, or FP&A type projections?
FP&A you might try Fathomhq.com; that can give you some planning insights.
B&P typically they're in whatever GL module you're using.
BOM analysis Excel works just fine.
I'm guessing you need something deeper?

Typically, start-ups lack cash to burn. Excel is the tool of choice. Of course, it's like anything else. If you're not expert at Excel and at forecasting, don't expect a scalable output. I'm happy to discuss if you need more help.

I prefer to use a Cash Flow Projection Excel spreadsheet. This allows you to plan ahead and adjust accordingly the revenue and expenses you anticipate you will have. I suggest that you plan in detail your first year and make sure you track and adjust as you go along.

One word; "Excel".

J.D. Floyd

Ditto, Excel

Agreed: Excel. There are always operating plan templates floating around, some good, some simply pretty. The useful thing about building from scratch in Excel (after you've looked at some instructive examples) is that it forces an entrepreneur to take a disciplined look at both cost and revenue drivers. The exercise of building a bottom-up model helps quickly find the most influential variables in the mix, which often are not what is expected, and the next ten important variables that are impossible to capture with some of these simplifying tools. Tedious, no doubt, but cheap and requires real pencil sharpening to get right, so the exercise.

And again: Excel.