Your severance is composed of three parts.
1 Two weeks/year with 35 weeks max. Severance base pay is calculated by adding base pay to target STI (10, 12 or 20%). Eg: If actual base pay is 80 K and STI is 12%, then severance base pay is 89.6 K
2 Unused and accrued vacation time ( unused personal hours are not paid in most states)
3 Pro-rated STI. For this, lower threshold rate is used instead of higher target rate.
Saw this in an old thread, thought it needed a bump, as people are always looking for this info. Clearly and precisely put, thanks @ONyCBmm-clse.