From Longman Dictionary of Contemporary Englishfactor something ↔ in (also factor something into something) phrasal verb technicalCOUNT/CALCULATEto include a particular thing in your calculations about how long something will take, how much it will cost etc → factor→ See Verb table
Examples from the Corpus
factor in• However subsequent research has shown that both negatives and passives are used in response to the presence of particular pragmatic factors.• Mrs Thatcher's unwilling departure was the result of a combination of factors.• There are always human factors at play in any relationship.• A sample of these present-value factors is presented in Exhibit 11. 3.• But ceremonial and precedence none the less remained until well into the eighteenth century a factor of importance in international relations.• The combination of climatic factors results in late flowering of many species in relation to their counterparts elsewhere.• The laws hold only as long as no other factors enter in, which might modify them in particular cases. 