The Dutch striker has found the target 18 times in 23 Premier League appearances and thrice in the Champions League.
"Not really well," The Guardian quotes the 29-year-old as saying when asked about his success at Old Trafford so far.
"It is going well but if you start to believe it's going well, you're going down. When I look back at those last 10 games it's a good step but to me it should have been 10 games, 14 or 15 goals. At least four or five I shouldn't have missed."
Van Persie joined United from Arsenal last summer.