I will likely be applying for PhD programs in mathematics. Several of the schools I intend to apply to state that they require ‘a minimum of 3 letters’. Presently, I have three solid letters from well known professors in my current institution, as well as a fourth letter from a professor from a different institution, with whom I’ve conducted research. Is it acceptable if I send four letters to these programs? Will it have any sizable positive/negative impact on the application? My main reason for sending the fourth letter, is because I feel it would highlight a specific research experience, and add credibility. Thanks!

  • 3
    If it says "a minimum of 3 letters" then you should be allowed to send a centillion letters, especially if they are serious about mathematics.
    – md2perpe
    Aug 9, 2020 at 14:12
  • When you wrote "a minimum" did you actually mean "a maximum"? Aug 9, 2020 at 16:16
  • @md2perpe A set can have only one member, and it will have a minimum. So, I don't see how they would be less serious about mathematics if they only wanted 3 letters. Aug 9, 2020 at 17:04
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    I don't get this at all (the question, and most of the answers). What is unambiguous about "a minimum of three letters"? Of course you can send four letters!
    – TonyK
    Aug 9, 2020 at 18:37
  • 1
    @RedGrittyBrick No, I meant a ‘minimum’ as the question states.
    – Geometer
    Aug 10, 2020 at 2:24

4 Answers 4


The first criterion, of course, is that if a particular institution's application intsructions communicate that only three letters should be sent, then abide by that. For the ones that say "at least three" or the like:

To be honest, in practice it really depends on the internal details of each university's application storage system and how it lets reviewers view applicants' files—and this can vary wildly from place to place. At my institution, if you have four letters of recommendation, they will all be visible when I look at your file. In other places, their online portal might have specific spots for three letters and no more (I would hope such institutions would make it clear in their instructions that only three letters should be sent).

As someone who has reviewed graduate applications for nearly twenty years, I can tell you that if my file system allows me to see the letters, I will read all the letters if I am interested in an applicant. (Well, I probably wouldn't read ten letters … but certainly four.) If you have reasons to believe that the letters will offer complementary perspectives on your excellence, I would use them all.

  • Thanks for your response. That makes sense. The only reason I want to send the fourth letter, is that one of the schools states that it does not go through one’s research work, and any such work should be mentioned in one’s SOP and letters of recommendations. Given that the SOP is one’s own word and thus not the most reliable, I think letters addressing this are a better option.
    – Geometer
    Aug 9, 2020 at 3:48
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    I would think that the fourth letter (the person you've conducted research with at a different institution) may actually be one of the most relevant ones, and maybe you should prioritise it over the other 3 (if you apply anywhere that limits the number of letters)
    – DavidW
    Aug 9, 2020 at 16:22
  • @DavidW Thanks for your response. I certainly agree that a recommendation from a faculty from an outside institution could help. However, I cannot forsake sending the other three letters, as they are simply too strong. Also, they have connections at the institutions I intend to apply to. I think I should only send the fourth letter to a handful of schools, which accept more than 3.
    – Geometer
    Aug 10, 2020 at 2:27

You should email the institution to which you are applying and ask their graduate admissions team if they would accept more than three letters. Whether it’s acceptable, irrelevant, or above a threshold to send more than 3 letters is subject to the preferences of the institution to which you are applying.

  • Thanks for your response. Some websites list that they allow more than 3 letters. I was just concerned about whether this would harm the application, as I don’t control the relative strength of the fourth letter.
    – Geometer
    Aug 8, 2020 at 17:46
  • 1
    Do not email if the answer is in the instructions, as stated in the question. Aug 10, 2020 at 0:19
  • @AnonymousPhysicist Yes, I don’t think I should. Emailing unnecessarily might hurt my application.
    – Geometer
    Aug 10, 2020 at 2:28

A problem you might encounter if they will only accept three and you send more, is that the might just ignore or throw out some of them. They might throw out the ones(s) you most want them to keep in such a case.

Unless you hear otherwise from an institution, stick to their requirements.

Some of the rules are to limit the work they have to do in evaluation, and some of it is just establishing fair rules for all applicants.

  • Thanks for your response. I just felt that this would add another dimension to my application, explaining the external research I conducted. Some of the schools state they at least need 3 letters. This could be construed as allowing more than 3 right?
    – Geometer
    Aug 9, 2020 at 3:02
  • 1
    @Geometer in that case I would assume they would read your 3 weakest letters and bin the rest.
    – emory
    Aug 9, 2020 at 3:20
  • 2
    How would they gauge that without having chosen the letters first?
    – Geometer
    Aug 9, 2020 at 3:45
  • @emory It is kind of a CS way to think about it, them reading the three worst letters out of the four is the worst-case scenario. That it could happen warrants consideration. Aug 9, 2020 at 23:35
  • @Geometer They would not, but if it is their policy to only read 3 letters then you surrended an element of control to a random process. I really think you should ask them. If they are not going to read more than 3 letters then send them your 3 strongest letters. If they will read more than 3 letters, it is more complicated.
    – emory
    Aug 10, 2020 at 1:24

Having worked in various universities in all sorts of different roles, from being a systems programmer to teaching etc., I would go to the department's office at first. These are the people who send out letters, open the mail and, usually, are the ones who calm down students who are late with submissions - although they can't and won't break the rules.

In fact I would phone them. Or even visit! I did this a few times and by making a personal connection I had a running start. For example I visited one institution without any appointment. Someone asked if they could help me. It turned out that they were a senior member on my interview panel and were impressed by my making the effort. I got the job and had many enjoyable years.

Phone call

"Hello, I'm sure you are busy so I hope you don't my asking. I'm planning to apply for X and I notice that three letters of recommendation are asked for. Would it be unusual to submit four?"

Anyone who has worked in that office for less than a year will ask a more experienced staff member.

Either they will answer or they will tell you who is best to talk to. This will most likely be the lecturer/prof who is overall responsible for intake.

Say: "Oh I don't want to bother them. Do you think it would be alright?"

There is a good chance they will arrange a brief phone conversation with the person. You will end up discussing your aims and interests as well as mere conventions.


If you meet indifference or even hostility at any point when asking for information, this will tell you something something about the department and how it is run. Personally I would only want to go to a friendly place and would cross anything else off my list.

By contacting and talking to people, you change from being paperwork to being a human being. They will notice your application when it lands on their desk.

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