According to an update from administrators Zolfo Cooper, the group, which was led by Peter Ellis, was previously lent £27.1m by Allied Irish Bank, but its sites and property were only worth £15.1m when it was placed into administration, a shortfall of £12m.
The value of the sites and land has since dropped by just under £100,000.
Creditors and staff have been left out of pocket by a combined £11.8m.
Suppliers, including breweries and councils, were left owed around £780,000, with Molson Coors owed £250,000, followed by Heineken £41,000 and Waverley £32,000.
Calco operated 79 managed and tenanted pubs across the Midlands and northern England, with most sites understood to be freehold. It was placed into administration due to “difficult market conditions”.
Zolfo Cooper said it would continue trading the sites and assess all possible opportunities for the business in due course.
Zolfo said it was confident that it would be able to secure the future of the business.