rules for sale of primary residence

[irene]

what are the rules for sale of a primary residence if it was owned for four years and lived in for 2 years

[Dude]

lived in for 2 of the last 5 years

[RWG1950]

Believe the section 121 exclusion rules require :
1. the taxpayer used the dwelling as his/her principal residence for at least a two year period during the preceeding 5 year period
2. no section 121 exclusion was used by the taxpayer during the prior two year tax period
Qualifying sellers of section 121 property can exclude gains on the sale of $ 250,000 (for singles) and $500,000 (MFJ).

[TaxGuyBill]

Was it used as a Principal Residence AFTER the non-lived in period? Or did it start off as two (or more) years as a Principal Residence, then change to a non-Principal Residence?