Made this mistake once and i'm posting so others don't repeat it.
When you go from W2 contractor (through a staffing agency) or 1099 to full-time employee, the headline base salary is not an apples-to-apples number. Here's the math I use before I name a number in negotiations.
Start with your all-in contractor rate: If you're 1099 at $120/hr, 40 hrs/week, 48 working weeks a year = $230,400 gross. But you pay both halves of FICA (~15.3% up to the wage base, ~2.9% above), and you have zero benefits. So employer-side FICA alone costs you roughly $17k. Add $20-25k for health insurance for a family. That's $37-42k you never see on a W2.
Flip it: if a company offers you $180k base + 15% bonus + standard health benefits (they pay ~$15k of that), the true economic comparison is $180k + $27k bonus target + $15k benefits = ~$222k equivalent. Suddenly your $230k gross 1099 rate looks different.
The multipliers I've seen cited are wrong for most people. The "1099 to W2 divide by 1.4" rule only applies if your contract rate includes the agency margin, you have no benefits, AND you're full-time year round. On a direct contract with full utilization, divide by 1.25 is closer.
Equity math matters more at certain company stages. At a Series B with a fresh 409A, $200k in RSUs might be worth $0 or might vest into something real. Model both outcomes before you decide the base salary floor.
What I actually said in my last FTE negotiation: I told the recruiter I had modeled my all-in contractor equivalent and wasn't looking to take a step down in total economic value. I asked them to walk me through the benefits details before we talked base. That one question usually buys a couple rounds of back-and-forth without you having to anchor a number.
Anyone else been through a contractor-to-FTE conversion recently? Curious if the market is moving at all on signing bonuses to offset the transition.