The frequency at which you need to change your transmission fluid can vary depending on the type of vehicle you have and the manufacturer's recommendations. In general, it's a good idea to consult your vehicle's owner's manual for specific guidance, as it will provide you with the manufacturer's recommendations for your particular make and model.

That said, here are some general guidelines:

Regular Maintenance Schedule: Many manufacturers recommend changing automatic transmission fluid (ATF) every 30,000 to 60,000 miles (48,000 to 96,000 kilometers) under normal driving conditions. For manual transmissions, the interval may be longer, typically around 60,000 to 100,000 miles (96,000 to 160,000 kilometers).

Severe Conditions: If you drive your vehicle under severe conditions, such as towing heavy loads, driving in extreme temperatures, or stop-and-go city driving, you may need to change the transmission fluid more frequently. Some severe-duty schedules suggest changing ATF as often as every 15,000 miles (24,000 kilometers).

Older Vehicles: For older vehicles with high mileage, it might be a good idea to change the transmission fluid more often, as ATF can deteriorate over time and with use.

Inspect the Fluid: It's a good practice to regularly check the condition and level of your transmission fluid. If the fluid appears dirty, has a burnt smell, or is discolored, it's a sign that it may be time for a change.

Flush or Drain and Fill: Some vehicles have a drain plug, while others require a complete transmission flush. The method you choose can impact the cost and effectiveness of the fluid change. Be sure to follow your vehicle manufacturer's recommendations.

Keep in mind that failing to change the transmission fluid at the recommended intervals can lead to problems with your transmission, reduced performance, and even costly repairs. Regular maintenance, including changing the transmission fluid, can help ensure the longevity and reliability of your vehicle's transmission system. Always consult your owner's manual or a qualified mechanic for guidance specific to your vehicle.