From Longman Dictionary of Contemporary Englishadd something ↔ in phrasal verbto include something with something else Don’t forget to add in the cost of your time. → add→ See Verb table
Examples from the Corpus
add in• But for today, the numbers do not quite add up.• Ivester will remain chief operating officer for the time being, a spokeswoman added.• James Boone added 19 and Marcus Millinder added 18.• NYT-05 - 18-96 2238EDT Since the season opened with four productions in February, two more shows have been added.• Since the season opened with four productions in February, two more shows have been added.• Chick said Saturday, adding that in retrospect, the focus on HMOs alone was too narrow.• As will be seen, autonomy in water supply and sewage were added later in the design.• To these we have to add distortions in the response of the subject of the investigation. 