Assuming no cashflow, it's obviously not possible for two people in the same investments to have different performances over the same period.

However, if you incorporate cashflow into the calculation, as the IRR does, the performance won't necessarily be the same for two people -- one can even be up while the other is down.

For example, suppose that over the last 60 days, the underlying portfolio has risen by 10%, but in the middle of that, there was a massive crash that we have since recovered from. If somebody sold out a significant amount at the crash, their overall IRR over the 60 days might show depreciation, even though yours shows appreciation.

Or alternatively, suppose that there was a huge peak in the middle of the 60 days and somebody else invested a large amount of money there. In this case again, their IRR might show depreciation even though yours shows appreciation for the same 60 days.

I will leave this is an exercise, but it's possible to construct a set of cash flows such that the IRR would both show appreciation and not do so. As I mentioned, the IRR is not necessarily a unique value, and when it's not, all values are equally correct; you can't just choose the one you like most.

The IRR is really not a very meaningful metric to use to compare to other members on this forum, for reasons I explained in

my previous post. If you use time-weighted returns instead, it will be the same as other members with the same portfolio regardless of cashflow decisions, assuming you quote it for the same time period.