Hundreds of witnesses have given testimony to the inquiry that has been examining allegations of historical abuse and neglect.
A report is expected next year.
The HIA was set up in 2013 to investigate child abuse in residential institutions in Northern Ireland over a 73-year period, up to 1995.
Analysis - BBC News NI's Kevin Sharkey
Men and women who were vulnerable children in care in Northern Ireland between 1922 and 1995 have appeared before the inquiry to give accounts of their childhood abuse.
Now middle-aged or elderly, they travelled to Northern Ireland from across the UK and Ireland.
Many others gave evidence from around the world, particularly from Australia.
Now they must all wait until the final report is given to politicians at Stormont, six months from now.
Ministers will then decide how to respond to a number of issues, including compensation.
These included a range of institutions, run by the church, state and voluntary sector.
It has been led by retired judge Sir Anthony Hart.
Public hearings at the Historical Institutional Abuse Inquiry (HIA) come to an end on Friday after two and a half years.