then designate old house to 2019, from 2006 to 2019 owned 14 year, plus 1 = 15, old house owned 15 years, 15/15=1, no capital gain, designate new house from 2020. if you sell new house in 2030, from 2020 to 2030 total 11 years, plus 1 =12,owned from 2019 to 2030 = 12 years, 12/12 = 1 no capital gain.