The more general answer is that cell updates could just keep going forever, never settling down, or at least taking a long time to settle down. There isn't a g

The more general answer is that cell updates could just keep going forever, never settling down, or at least taking a long time to settle down. There isn't a good one-size-fits-all way to resolve this. Plus, these sorts of structures are most likely typos by the people writing the spreadsheets. The more specific answer is that Excel performs a topological sort on the cell dependency graph in order to update cells in an efficient order. Edit: as someone else has pointed out, if you really want cycles, there's an option to tell Excel how to terminate computation for your particular infinite loop use case.