Biggest improvements from one season to the
next (based on regular season win percentage):
                                          Change in
       Franchise                            win %
  1 Arizona Diamondbacks    1998 -> 1999      21.6   (40.1  ->  61.7)
  2 Boston Red Sox          1945 -> 1946      21.4   (46.1  ->  67.5)
  3 Atlanta Braves          1935 -> 1936      21.3   (24.8  ->  46.1)
  4 Philadelphia Phillies   1904 -> 1905      20.4   (34.2  ->  54.6)
  5 Baltimore Orioles       1988 -> 1989      20.2   (33.5  ->  53.7)
  6 Philadelphia Phillies   1961 -> 1962      19.8   (30.5  ->  50.3)
  7 San Francisco Giants    1992 -> 1993      19.2   (44.4  ->  63.6)
  7 Tampa Bay Rays          2007 -> 2008      19.2   (40.7  ->  59.9)
  9 Baltimore Orioles       2021 -> 2022      19.1   (32.1  ->  51.2)
 10 Pittsburgh Pirates      1917 -> 1918      18.9   (33.1  ->  52.0)
 10 St. Louis Cardinals     1913 -> 1914      18.9   (34.0  ->  52.9)
 12 Athletics               1946 -> 1947      18.8   (31.8  ->  50.6)
 13 Kansas City Royals      2023 -> 2024      18.5   (34.6  ->  53.1)
 13 San Diego Padres        2019 -> 2020      18.5   (43.2  ->  61.7)
 15 Cincinnati Reds         1937 -> 1938      18.3   (36.4  ->  54.7)
 15 Minnesota Twins         1911 -> 1912      18.3   (41.6  ->  59.9)
 17 Boston Red Sox          1911 -> 1912      18.1   (51.0  ->  69.1)
 17 Philadelphia Phillies   1928 -> 1929      18.1   (28.3  ->  46.4)
 19 Arizona Diamondbacks    2010 -> 2011      17.9   (40.1  ->  58.0)
 19 Atlanta Braves          1952 -> 1953      17.9   (41.8  ->  59.7)
 19 Atlanta Braves          1990 -> 1991      17.9   (40.1  ->  58.0)
 19 Detroit Tigers          2003 -> 2004      17.9   (26.5  ->  44.4)
 19 Athletics               1979 -> 1980      17.9   (33.3  ->  51.2)
 24 Athletics               1908 -> 1909      17.7   (44.4  ->  62.1)
 24 San Francisco Giants    2020 -> 2021      17.7   (48.3  ->  66.0)

    Last season:
    Toronto Blue Jays       2024 -> 2025      12.3   (45.7  ->  58.0)
    Chicago White Sox       2024 -> 2025      11.7   (25.3  ->  37.0)
    Miami Marlins           2024 -> 2025      10.5   (38.3  ->  48.8)
    Chicago Cubs            2024 -> 2025       5.6   (51.2  ->  56.8)
    Los Angeles Angels      2024 -> 2025       5.5   (38.9  ->  44.4)
    Boston Red Sox          2024 -> 2025       4.9   (50.0  ->  54.9)
    Athletics               2024 -> 2025       4.3   (42.6  ->  46.9)
    Cincinnati Reds         2024 -> 2025       3.7   (47.5  ->  51.2)
    Seattle Mariners        2024 -> 2025       3.1   (52.5  ->  55.6)
    Milwaukee Brewers       2024 -> 2025       2.5   (57.4  ->  59.9)
    Texas Rangers           2024 -> 2025       1.9   (48.1  ->  50.0)
    Philadelphia Phillies   2024 -> 2025       0.7   (58.6  ->  59.3)
    Detroit Tigers          2024 -> 2025       0.6   (53.1  ->  53.7)
    San Francisco Giants    2024 -> 2025       0.6   (49.4  ->  50.0)