NFL : Biggest year to year improvements 

                                             Change in
    All Time:                                 win %
  1 Indianapolis Colts       1998 -> 1999     0.625   (0.188 -> 0.813)
  1 Miami Dolphins           2007 -> 2008     0.625   (0.063 -> 0.688)
  3 New England Patriots     2024 -> 2025     0.589   (0.235 -> 0.824)
  4 New England Patriots     1975 -> 1976     0.572   (0.214 -> 0.786)
  5 Indianapolis Colts       1974 -> 1975     0.571   (0.143 -> 0.714)
  6 Dallas Cowboys           2015 -> 2016     0.563   (0.250 -> 0.813)
  6 Indianapolis Colts       2011 -> 2012     0.563   (0.125 -> 0.688)
  6 Kansas City Chiefs       2012 -> 2013     0.563   (0.125 -> 0.688)
  6 Los Angeles Rams         1998 -> 1999     0.563   (0.250 -> 0.813)
  6 Pittsburgh Steelers      2003 -> 2004     0.563   (0.375 -> 0.938)
  6 San Francisco 49ers      2018 -> 2019     0.563   (0.250 -> 0.813)
 12 Jacksonville Jaguars     2024 -> 2025     0.530   (0.235 -> 0.765)
 13 Indianapolis Colts       1991 -> 1992     0.501   (0.062 -> 0.563)
 13 New York Jets            1996 -> 1997     0.501   (0.062 -> 0.563)
 15 Chicago Bears            2000 -> 2001     0.500   (0.313 -> 0.813)
 15 Los Angeles Chargers     2003 -> 2004     0.500   (0.250 -> 0.750)
 17 Cincinnati Bengals       1987 -> 1988     0.483   (0.267 -> 0.750)
 18 Washington Commanders    2023 -> 2024     0.471   (0.235 -> 0.706)
 19 Carolina Panthers        2014 -> 2015     0.469   (0.469 -> 0.938)
 19 Cleveland Browns         2017 -> 2018     0.469   (0.000 -> 0.469)
 21 Tennessee Titans         1966 -> 1967     0.465   (0.214 -> 0.679)
 22 Miami Dolphins           1969 -> 1970     0.464   (0.250 -> 0.714)
 23 Las Vegas Raiders        1981 -> 1982     0.451   (0.438 -> 0.889)
 24 Atlanta Falcons          2007 -> 2008     0.438   (0.250 -> 0.688)
 24 Baltimore Ravens         2005 -> 2006     0.438   (0.375 -> 0.813)
 24 Denver Broncos           1990 -> 1991     0.438   (0.312 -> 0.750)
 24 Detroit Lions            1979 -> 1980     0.438   (0.125 -> 0.563)
 24 Houston Texans           2013 -> 2014     0.438   (0.125 -> 0.563)
 24 Houston Texans           2017 -> 2018     0.438   (0.250 -> 0.688)
 24 Los Angeles Chargers     1991 -> 1992     0.438   (0.250 -> 0.688)
 24 Los Angeles Rams         2016 -> 2017     0.438   (0.250 -> 0.688)

    Last season:
    New England Patriots     2024 -> 2025     0.589   (0.235 -> 0.824)
    Jacksonville Jaguars     2024 -> 2025     0.530   (0.235 -> 0.765)
    Chicago Bears            2024 -> 2025     0.353   (0.294 -> 0.647)
    San Francisco 49ers      2024 -> 2025     0.353   (0.353 -> 0.706)
    Denver Broncos           2024 -> 2025     0.236   (0.588 -> 0.824)
    Seattle Seahawks         2024 -> 2025     0.236   (0.588 -> 0.824)
    Carolina Panthers        2024 -> 2025     0.177   (0.294 -> 0.471)
    Cleveland Browns         2024 -> 2025     0.118   (0.176 -> 0.294)
    Houston Texans           2024 -> 2025     0.118   (0.588 -> 0.706)
    Los Angeles Rams         2024 -> 2025     0.118   (0.588 -> 0.706)
    New Orleans Saints       2024 -> 2025     0.059   (0.294 -> 0.353)
    New York Giants          2024 -> 2025     0.059   (0.176 -> 0.235)
    Dallas Cowboys           2024 -> 2025     0.029   (0.412 -> 0.441)