Your toilet is cracked or leaking
A cracked or leaking toilet can lead to continuous and expensive repairs. Not only can a toilet leak lead to major damage to the flooring but can also overtime cause mould growth on your bathroom walls and skirting boards which eventually will need redecorating. We sometimes take no notice to small leaks that at present are not causing a major issue, however even the slightest leak will eventually lead to a massive water bill. Cracked toilets if not replaced can eventually cause a blow-out which causes extensive damage to the surrounding area and an extremely hefty bill. When you notice first signs of a cracked/leaking toilet you should consider an upgrade.
Your toilet requires extensive repairs
If you are faced with multiple issues with different components in and around your toilet, it would be the best option to look into obtaining a whole new toilet as this will definitely help you financially, especially of your current toilet is rather old. Shop around to gain some quotes and compare with the costs that you would be out on replacing parts etc, to see which one works out best.
You are remodeling your bathroom
If you are considering a remodel of your bathroom it may be the best time to also update your toilet, as the remodelling process normally involves taking up the flooring and sometimes installing new pipework which means also taking out the current toilet in order to lay down a new supply. Remodeling can also involve sink/basin/bath upgrades so you would not want the new fittings to outshine the old toilet.