You generally change spark plugs between about 30,000 and 100,000 miles, but the exact interval depends on your car and the type of plug, so the first rule is: always follow your owner’s manual.

Typical change intervals

  • Many manufacturers recommend changing spark plugs roughly every 30,000–50,000 km (about 20,000–30,000 miles) for standard plugs.
  • Long‑life platinum or iridium plugs in modern cars often last 60,000–100,000 miles or more if everything else is in good condition.
  • Some vehicles have model‑specific intervals; for example, certain Toyotas list spark plug service anywhere from about 60,000 to 120,000 miles.

What really decides the interval

  • Plug type :
    • Copper: shorter life, around 20,000–30,000 miles.
* Platinum/iridium: much longer life, commonly up to ~100,000 miles.
  • Driving conditions: frequent short trips, stop‑and‑go traffic, towing, or poor‑quality fuel can all shorten plug life and justify earlier changes.
  • Vehicle design: some engines run plugs hotter or are more sensitive to wear, so their factory schedule may be more conservative.

Signs you should change them sooner

  • Rough idle, shaking, or “stumbling” at stops.
  • Sluggish acceleration or the car feeling noticeably down on power.
  • Engine misfires, hard starting, or a flashing/check‑engine light related to misfire codes.
  • Worse fuel economy than usual without another clear cause.

If any of these show up, it is reasonable to inspect or replace the plugs even if you have not hit the official mileage interval yet.

Simple rule of thumb

  • Check your owner’s manual and use that interval as your baseline.
  • If you do mostly gentle highway miles with a newer car and long‑life plugs, staying close to the upper range (60k–100k miles) is often fine.
  • If you drive hard, tow, idle a lot in traffic, or do many short trips, consider inspecting or changing closer to the lower end of the range (20k–40k miles) or whenever symptoms appear.

Information gathered from public forums or data available on the internet and portrayed here.