When a trademark office compares two names, and when a brand's lawyer decides whether to send a complaint, they look at four things. Your name will be judged on the same four, so test it on them first.
Sight
How the two marks look written down. Length, first letters, and the overall shape matter more than the middle. "Zentra" and "Zentro" look alike. "Zentra" and "Ventra" too, because the eye reads the ending. A different first letter helps; a different last letter helps less than sellers expect.
Sound
How they are spoken. This one catches people because spelling tricks do not change it. "Kwik" is "Quick". "Phresh" is "Fresh". "Lyte" is "Light". Phonetic similarity is enough on its own for a refusal in most offices, and the checker scores it separately for that reason.
Meaning
Whether the marks call the same idea to mind. "Sun King" and "Roi Soleil" are the same mark in two languages. A translation is not a new name.
Goods
Whether the products are close enough that a buyer might think they come from the same source. Identical names can coexist in unrelated goods. Similar names in the same class usually cannot. This is why the checker asks for your class before it scores.
Reading the score
The TMAtlas Risk Score puts these together into one number with the reasons written out. Above 72, the closest mark is near-identical in your goods and live. I would not proceed. Between 45 and 71, the marks share sight or sound but differ somewhere that matters; read the reasons, look at the owner and the goods, and decide. Below 45, the nearest marks differ in text, goods or status.
The reasons are the useful part. "Sounds the same when spoken" next to "same goods class" is the pattern behind most refusals and most takedowns. "Different goods class" next to "expired" is a name you can probably use.
The one-letter myth
Changing one letter from a registered mark is the most common thing sellers do, and it is close to useless. Examiners are trained to see through it, and rights owners search for exactly those variants. If your name needs a letter changed to avoid a live mark in your class, the name is the problem.