[1] This competition consists of a first stage with all the teams then proceed to a promotion or relegation series depending on their performance.

The winners of each series will be automatically promoted to Liga Portugal 2 and will face each other in a neutral venue to determine the champion.

[3] Cova da Piedade failed to produce valid licensing documentation to compete in the 2021–22 season of the Liga Portugal 2, so they had been relegated by the Portuguese Football Professional League to Liga 3.

[4] Leça failed to produce valid licensing documentation to compete in the 2021–22 season of the Liga 3, so they had their promotion denied by the Portuguese Football Federation.

As a result, Sanjoanense (3rd place in Promotion Serie 3) were invited to play in the third tier for the 2021–22 season.