There are several synonyms for the phrase "did the top of head". One option is "off the top of my head", which means giving an answer without much thought or research. Another synonym is "spontaneously", which indicates doing something without pre-planning or preparation. "Instinctively" is another option, which means doing something based on gut feelings or intuition. Additionally, "impulsively" can be used to describe doing something on a whim or without much thought. Finally, "involuntarily" can be used to describe an action done without conscious control or intention. Overall, there are many different synonyms that can be used to describe doing something without much thought or planning.