TWELVE teams, eight finals spots. It's basic mathematics, but there's nothing simple about it.

Welcome to the final month of the home and away season, which is set to play host to one of the most thrilling finishes in recent memory.

Ladder leader Sydney has been clearly the best team in the competition from the season opener, but recent speed wobbles have given the chasing pack – including Carlton, Fremantle and a resurgent Brisbane – reason to believe the Bloods can be stopped.

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Meanwhile, the Western Bulldogs and Hawthorn have refashioned themselves into high-scoring, free-flowing offensive juggernauts while Geelong's blend of youth and wily experience – and a healthy home-ground advantage – shouldn't be discounted.

GWS and Port Adelaide look in good shape to return to September after shaking off their mid-season slumps, while the Victorian quartet of Essendon, Collingwood, Melbourne and Hawthorn all still harbour some hope of finals action despite suffering more losses than they'd like.

It's all set up for a huge final four rounds. Here are the 17 games that matter most, and when the contenders will face their biggest games.

ROUND 21

Key matches
Western Bulldogs v Melbourne
Collingwood v Carlton
Port Adelaide v Sydney
GWS v Hawthorn
Essendon v Fremantle

It's a big weekend for…
Essendon, Collingwood and Port Adelaide. It's the last-chance saloon for the Bombers, who could have their season effectively ended with a loss to Fremantle at Marvel Stadium. Defeat could leave Essendon a game and a half outside the top eight with clashes still to come against top-two sides Sydney and Brisbane. The 12th-ranked Pies just need to keep winning every week to stay in the race, while the Power could go a long way to shoring up their finals berth with a win at home against the faltering Swans.

ROUND 22

Key matches
Sydney v Collingwood
Brisbane v GWS
Fremantle v Geelong
Melbourne v Port Adelaide
Carlton v Hawthorn

It's a big weekend for…
Melbourne, Geelong, Carlton and Hawthorn. This looms as a monster round for determining the make-up of this year's top eight. The Demons simply have to win this MCG clash against a non-Victorian side, given there's a trip to the Suns' near-impregnable fortress the following week. If the Cats can scrape a win in the west over fellow top-four hoepful Fremantle, they'll be in great shape to claim the double chance. And the Sunday afternoon clash between the Blues and Hawks is set to be an old-fashioned MCG blockbuster, with the Hawks striving for an unlikely September return and the Blues keen to lock in their top-eight spot.

ROUND 23

Key matches
Essendon v Sydney
GWS v Fremantle
Collingwood v Brisbane

It's a big weekend for...
Sydney, Brisbane and GWS. The current top two hit the road to face big Victorian clubs in two tasty match-ups that could well cement their double-chance hopes and potentially lock in home finals in the first week of September. The Swans will face an Essendon side whose season could be done, while the Lions return to the 'G for a Grand Final rematch against a Magpies side that is a fair way off the unit that stormed to last year's premiership. And in Sydney, the Giants host the Dockers in a match that should have a significant bearing on the top four. There's a plausible scenario in which all teams from third to eight on the ladder are within one win of each other, setting up a massive final weekend of the home and away season.

ROUND 24

Key matches
Brisbane v Essendon
Melbourne v Collingwood
Western Bulldogs v GWS
Fremantle v Port Adelaide

It's a big weekend for...
Everyone, really, but especially the Western Bulldogs and Fremantle. If a week is a long time in footy then a month is a near-eternity, and predicting the ladder from this far out is fraught with danger. However, the two most pivotal games are set to be played in Ballarat and Perth. The Bulldogs host the Giants in a clash that could define each team's hopes of a top-four finish, or a home elimination final. And in the west, the Dockers will likely be seeking the double chance with victory over the Power, which in turn will be desperate for a home-ground advantage in the first week of the finals.