Start with the manufacturing code
Use the DOT tire date-code guide to locate and interpret the week and year. Record the code for each tire because replacements may have different dates.
Inspect more than age
Look for cracking, deformation, bulges, exposed material, repeated pressure loss and unusual vibration. Spare tires also age even when tread appears unused.
Follow applicable manufacturer guidance
Replacement guidance can vary by tire and vehicle manufacturer. TireHelp does not assign a universal lifespan from date alone.