Because his mother Lynne Smith, from Billing, often has more work for him to do in the form of autographs for some of his thousands of fans.
Lynne, who also runs a shop called The Accessory Room in Kingsley, Northampton, uses any quiet moments she has to handle the hundreds of requests sent to Matt. Lynne explained: "Matt is really pleased and proud I have taken this on but obviously it is harder because when I see Matt I usually have a felt tip pen and 1,000 cards for him to sign. Every card that is sent out is personally signed by Matt and I think it is important to have that personal touch."
But what is it like to be on the receiving end of fan mail resulting from such a global phenomenon as Doctor Who?
Post is forwarded to Lynne from fans of all ages from all over the world – amounting to hundreds of letters each week – which must then receive a reply.
She said: "All I do is handle the signed autograph requests, all the fan mail goes to the BBC or his agent and it comes to a PO Box number to be picked up every week.
"I get a sack load every week, we are talking hundreds and now, because there is so much, I'm going through the backlog."
She continued: "Each letter you get has to be read from start to finish because these letters are important and what greater interest in doing it properly would there be other than from being his mother?"
Fan mail received has ranged from little children writing independently or entire school classes getting in some handwriting practice right up to Doctor Who fans in their 90s.
The breadth of ages seems to be a sign of how Matt has been helping win over younger generations to the show, as well as keeping the attention of the older, stalwart Doctor Who fans.
Lynne said: "It is a fan club, so people aren't going to send in derogatory letters, but I have been so happy to see the range of fans who have been writing in.
"I think the older generations perhaps go to the theatre and appreciate his acting skills. But there is a new audience coming along who liked the character and moments such as in the first episode when he has fishfingers and custard."
She added: "He is sometimes sent things and he has had cards for every occasion saying happy Easter or happy birthday or good luck. There are a lot of people who paint portraits for him and send in sketches."
And there are some signs that Matt has already achieved heart-throb status, with many letters coming from young girls aged 15 or 16.
Lynne said: "They say things like 'we think you are cool' and 'we think you are the best doctor'. I think they do think of him as a heart-throb. That makes me smile because to me he's just Matthew.
"A lot of the letters have been really aspirational, a lot of people want to be actors, then you get the letters from five or six-year-olds asking if he can come to their house for tea. He gets lots of invitations to fetes and schools and obviously he can't go to all of these.
"A lot of David Tennant fans have written in to say 'we were really sad when David Tennant left, but we think you are amazing'."
The fan letters are just a sign of the level of worldwide attention that Matt attracted when he took on the Time Lord role. And being suddenly plunged into the spotlight is something that Matt and his family have learned to handle.
Lynne said: "I have been completely surprised by it all. The problem is that, because he is my son, you don't think there will be all these people writing in, but I have been overwhelmed by the support for him.
"I don't mean that to sound silly, that is just how I feel. I have to separate Matthew as Matthew and the Doctor as the Doctor. He is our son, but also the 11th Doctor.
"It does affect you in the way that, when we are out with him, people will come up for autographs and pictures and, from that point of view, our level of privacy is probably different; but it is not me and my husband they are interested in, it is Matthew.
"I have to be honest and say he handles it so graciously and so well. He always has time for people and always gives people an autograph or photo as that is his role. He is proud of what he is doing and knows how to remain graceful and treat people with respect. There is nothing worse than people with stars in their eyes.