In　the　five-axis　flank　milling,　the　calculation　process　of　the　instantaneous　uncut　chip　thickness(IUCT)　is　complicated　because　of　the　motion　of　the　two　additional　rotational　axes.　To　focus　on　the　problem　that　the　IUCT　prediction　in　five-axis　milling　is　inefficient,　an　IUCT　calculation　method　considering　the　cutter　runout　effect　is　proposed　in　this　paper.　First,　the　geometry　model　of　the　cutting　tool　is　established,　and　the　coordinate　of　a　cutting　edge　point　can　be　obtained.　Then,　based　on　the　geometrical　relationship　of　two　adjacent　tool　positions,　the　analytical　solution　of　the　IUCT　can　be　derived.　Finally,　the　simulation　of　the　proposed　method　is　carried　out　to　validate　the　practicability　of　the　model.　The　results　show　that　the　proposed　model　can　achieve　good　efficiency　and　acceptable　accuracy　and　be　applied　to　milling　force　prediction.　©　2024　SPIE.