DATEDIFF incorrect - not sure why

Hi tamerj1 

Thanks. Yes I think you are right and this is the issue. However when I select the measure [End Lease Date] so that I can change the Format dropdown on the Ribbon to Date, I only have Text as an option and cannot change this.
How can I do so? The measure in full is:

End Lease Date = 
VAR _asOfDate = [As Of Date]
VAR _assetref = [asset reference]
VAR _leaseref = [Lease Reference]
VAR _unitref = MAX(Unit[Unit Reference])
VAR _tenantref = [Tenant Reference]
VAR _datein3months = EDATE([As Of Date],3)
RETURN
VAR _filter = 
FILTER(Lease_Unit,
     MAX(Lease_Unit[Lease.Tenant Reference]) = _tenantref &&
        AND (
            Lease_Unit[Lease.Expiration Date] >= _asOfDate,
            Lease_Unit[Lease.Commencement Date] <= _asOfDate
        )
            || Lease_Unit[Lease.Lease Status] IN { "Holding Over", "Month-to-Month" }
        && OR( 
            Lease_Unit[Lease.Termination Date] >= _asOfDate, 
        isblank(Lease_Unit[Lease.Termination Date])
        )
     )
VAR _terminationDate = CALCULATE(MAX(Lease_Unit[Lease.Termination Date]),_filter)
VAR _expirationdate = CALCULATE(MAX(Lease_Unit[Lease.Expiration Date]),_filter)
VAR _status = CALCULATE(MAX(Lease_Unit[Lease.Lease Status]),_filter)

VAR _targetdate = IF(NOT ISBLANK(_terminationDate), _terminationDate,  
                    IF(_status = "Holding Over" || _status = "Month-to-Month", _datein3months,
                    IF(NOT ISBLANK(_expirationdate), _expirationdate, 
                    _datein3months))) 

RETURN

FORMAT(_targetdate, "dd/mm/yyyy")

I had to put the FORMAT part at the end as it wasn't recognising anything as a date?