The Oxford Learners' Dictionaries website is an excellent, free resource. https://www.oxfordlearnersdictionaries.com/definition/english/factor-in?q=factor+in factor in - phrasal verb factor something in | factor something into something ​to include a particular fact or situation when you are thinking about or planning something Example Remember to factor in staffing costs when you are planning the project.

factor in verb (tr, adverb) mainly US to take account of (something) when making a calculation https://www.dictionary.com/browse/factor--in?s=t

Thank you so much for everybody, I understand! :)

Synonyms that could be used are "to account for", "to accomodate for", "considering" , "to prepare for the fact", "because there are many variables", and "in order to include". (Hopefully one of these made sense!!) It is used when one is doing a calculation, and explaining how it came to be. Here are some other example sentences that are easier to explain. "A decreased demand in gas (oil/petrol) was factored into the low price." This sentence means essentially that the lower demand of gas affected the price that it was selling for, decreasing it. "She forgot to factor in the price of tax, and was thus short (missing) the $2 needed to buy the shoes." This sentence means that the girl did not remember to calculate the price of tax, so she does not have enough money to buy the shoes.

'to factor in' is kind of like to consider in this context, but more causal - it works as a verb. for example, in order to factor in cost, i made a list of the things i need to buy (so that cost can be considered, you're making a list)