Almost every renovation has surprises. You open a wall and find old wiring, damp, poor previous work, or pipes where you didn’t expect them. If your budget is stretched to the last rupee or dollar with no space for surprises, these discoveries turn into stress and arguments.
Keeping even 10–15% aside as a contingency buffer changes the feeling of the whole project. When something unexpected appears – and it usually does – you can handle it without panic. You’re not forced into cheap, rushed decisions just to stay afloat.
It also gives you flexibility for small upgrades you might want mid-way, like slightly better hardware or lighting, without blowing everything up.
You may not end up spending the full buffer, which is a nice bonus at the end. But knowing it exists lets you breathe and keeps the relationship with your contractor calmer.