When something is uncertain we can use a buffer to smooth the impact of the variability.
Since internet speeds fluctuate video streaming services buffer the download to provide us with a smooth viewing experience (hopefully).
Some predictable expenses are uncertain in their exact cost, especially the further in the future they are. For example utilities, car servicing and home maintenance.
To help you absorb the impact of predictable item(s) being more expensive than planned include a buffer amount in your plan.
Start with 5% of your predictable commitments then increase to 10% over time.
A buffer for the variability in your predictable expenses helps minimise the chance you need to dip into your emergency savings for foreseeable expenses. (Emergency savings are for emergencies that you hope never occur.)
Your experience of managing your money will also be smoother.