got laid off from a 900-person company last year. initial severance offer was 6 weeks. ended up with 10 weeks plus extended benefits. not trying to make this sound like a big win because the whole situation was terrible, but i did learn something about what actually works.
what DOES move the number:
tenure. this is the strongest lever. most companies have an unpublished policy of 1-2 weeks per year of service. if you've been there 5+ years and you're getting 4 weeks, you can point to this norm directly. ask HR what the severance formula is.
transition costs. i had a specific child care situation where the layoff created a gap in my existing arrangements. i named a specific dollar amount it would cost me and asked if the company could bridge it. i got 2 additional weeks partly because i made the ask concrete.
role criticality / knowledge transfer. if you're the only person who knows how a critical system works and the company needs a transition period, that's leverage. offering to consult for a defined number of weeks at a day rate can also flip a termination into something better than the base offer.
unvested equity acceleration or extended window. see the post about vesting acceleration in this channel, but specifically: the exercise window extension for options is often a lower-cost ask for the company than cash severance. don't forget it.
what does NOT move the number:
"i have a mortgage" / "the market is bad right now" / "i've given so much to this company." emotional appeals don't get HR anywhere internally because they can't take them to finance as a justification. the ask has to have a business case or a factual norm behind it.
also: threatening to not sign and then signing three days later. the leverage exists before you sign. after you sign it's gone. know your deadlines. in most states you have 21 days to consider a separation agreement (45 days if it's a group layoff for ADEA purposes) and 7 days to revoke after signing.