The answer to 'when to replace toilet' is that you should typically replace your toilet every 15-20 years, or sooner if it is constantly clogging, leaking, or not flushing properly. Older toilets can become less efficient over time, using more water per flush and costing you more on your utility bills. Additionally, toilets that are cracked, chipped, or otherwise damaged should be replaced to prevent water leaks and potential water damage.
If your toilet is more than 15 years old and you are experiencing any of these issues, it's a good idea to consider replacing it with a newer, more water-efficient model. This can save you money on your water bill and help conserve water. However, if your toilet is in good working condition, there's no need to replace it just because of its age.