Experience has proven that this is an impossible question to answer accurately.
The major enemies of a flag are wind, sun and carelessness, the single greatest cause of flag deterioration.
No one can control the weather, but you can take care of your flag and lengthen its life.
Occasional washing in warm, mild, detergent water will prevent dirt and pollution from attaching to the fabric.
To prevent mildew, let your flag dry thoroughly before storing it.
Have your flag repaired at the first sign of fraying, do not wait for it to be blown to shreds.
Continuous day and night display will shorten a flag's life. If your flag is not illuminated at night, you should consider taking it down to appreciably lengthen its life.
Flags are manufactured to give maximum service in return for reasonable care and prudent use. Remember, no two flags receive identical wear.
Because weather conditions vary, wearing conditions vary and, consequently, the life of each flag is different. Your flag works hard. It shakes, it trembles, it drapes, it whips, it snaps, it bakes, it freezes, it ripples, it flutters, it furls, it twists, it flaps, it stains, it hangs! Is it any wonder that it needs to be replaced two or three times a year?
The best way we know to stretch your "flag dollar" is to have two flags; one flying and a clean one in reserve for special occasions.