The 2026 ISL1 is split into 2 phases. In the 1st Phase, each ISL1 teams plays Home-Away matches with the other 11 ISL1 teams twice, for a total of 22 regular season matches. In the 2nd phase, the 1st Phase teams ranked 1-6 play in the Championship Round. and the teams ranked 7-12 play in the Relegation Round. In each round, each team plays the other 5 teams in their group once for 27 total matches per team. Table ranking ties are broken by (1) goal difference, (2) total goals scored, (3) head-to-head points, (4) head-to-head goal difference, (5) head-to-head goals scored, (6) head-to-head away goals scored, (7) a playoff (only to decide the champion), then (8) a draw.

Not applicable.

At the end of the 2026 ISL1 season, the 5th and 6th place ISL1 Relegation Round teams will be relegated to the ISL2, and the 1st and 2nd place ISL2 teams will be promoted to the 2027 ISL1.