By Jim Donovan: Southwest has kicked off its 40th Anniversary with a big sale. Fares start at $40 each way and cover every city found both on the Southwest and AirTran destination maps.

Southwest’s fares are prorated based on distance. Flights of up to 450 miles are on sale for $40, one way while flights between 451 and 1,250 miles are on sale for $80 one way, and flights over 1,251 miles are $120 each way. Taxes and fees are not included in those fares.

You need to act quickly to lock in one of the sale fares. The sale ends Thursday at midnight PT, and the number of seats being sold at the sale fares are limited. The sale fares are good for travel from Aug. 23 through Nov. 16, though Fridays and Sundays are blacked out from the cheapest fares. Also, four days around the Labor Day and Veterans Day holidays are blacked out (Sept. 1, 5, and 6; and Oct. 10).

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