The biggest mistake is only counting visible items and forgetting all the “invisible” work and extras. People usually add up tiles, paint, cabinets and fixtures, then assume that’s more or less the total. But real renovations involve demolition, disposal, labour, hardware, adhesives, primers, electrical changes, plumbing fixes and a long list of small materials you never see in glossy photos.

Another classic error is not adding a buffer. Almost every project runs into something unplanned – a hidden leak, old wiring that isn’t safe, walls that are not straight, or design changes mid-way. If you don’t keep at least 10–20% aside as contingency, even normal surprises feel like disasters.

There’s also the “Pinterest problem”: liking high-end finishes while calculating costs on basic ones. If your heart is set on premium materials, your spreadsheet has to reflect that honestly.

A better way is to get detailed quotes from at least two contractors, ask them to break down all line items, and then still add a buffer. That way, you’re planning for reality, not for an ideal world where everything goes perfectly and nothing unexpected shows up.