Differences between "How are you?", "How are you doing?" and "How do you do?"

Question

What are the main differences between the three sentences written below? When should we use these greetings?

1. How are you?
2. How are you doing?
3. How do you do?

Answer 1

“How do you do” in modern American English is a formal noise made upon meeting someone. It rarely, if ever, indicates actual Interest in an answer. It can be acknowledged by repeating the same phrase back, or by saying “Very well, and you?”, to which the answer is also “Very well”. It can be abused as an opportunity to seize control of the conversation by interpreting it as one of the others, but that's rude.

“How are you” is an inquiry about the person's health, usually physical but mental/mood is included . Again it's often just a ritual, a friendly greeting, but it's not unreasonable to give a real answer to this one: “Great except for my allergies kicking up”, for example. Generally the answer should be brief, so the querant can decide whether they want to ask for more details or not. But in most cases, some version of “Fine, and you?” is the right ritual answer unless this is asked by a close friend or your doctor.

“How are you doing” is a more general inquiry about how your life is going. Depending on context and intonation, it can range from another ritual greeting (fine, and you?) to a deep expression of concern (which can be brushed off with the ritual answer or given a more meaningful response).

Exceptions abound, but those are the most common usage patterns in my dialect, anyway. (NE US)

Answer 2

The three forms of greetings are classed as pleasantries by language experts. Depending on context, and to whom you are speaking, each form of greeting has its own implication and meaning. But generally speaking they are all used when meeting a person, an acquaintance or even a dear friend.

How are you? (red line)
Perhaps the most common form of greeting or salutation today. Depending on context the person asking may be genuinely interested in hearing about the other person's wellbeing or health. In many cases the greeting is said as a way to open a dialogue or bridge an embarrassing pause in the conversation. With that said, it is often used as a means of polite introduction and can be quite formal; however, the person asking is not really interested in hearing about your medical history, he or she is only being polite. The usual reply (with all its variations) is: "Oh, I'm fine, thanks. And you?"

How are you doing? (green line)
Personally, I am less prone to use this expression myself, I believe its origins are American English and it is without doubt the friendliest, the most informal, and casual salutation. It is becoming increasingly popular as seen in the Ngram chart below. It popularity may partially be due to the character of Joey Tribbiani (played by Matt LeBlanc). He turned it into a catchphrase in the American sitcom Friends. Typical replies are: "Good", "I'm good", "I'm doing fine" and, possibly, followed with "And how are you doing?" The phrase is often written as: How are you doin'? Note the apostrophe substituting the last letter -g which is omitted in casual speech.

How do you do (blue line)
The most formal and polite form of greeting someone. Nowadays it is rarely said among acquaintances, friends and never between family members. Perhaps if you were introduced to the Queen or a member of the British Cabinet you might use the occasion to express this nicety. It sounds terribly British, and today it's often interpreted as being rather cool and aloof. It used to be the norm to repeat the salutation with the same exact words, "How do you do" without the rising intonation at the end.

The following Ngram chart displays the frequency of use. Please note however that it does not reflect how often native speakers say these greetings to one another, the chart should be seen as only an indication of popularity in print.

For further reference on the usage of "How are you?" and "How do you do?" see the BBC website: Learning English

How do you do? is very formal and is not used very much, especially by younger people, these days. It may be used on first meeting and accompanied by a formal handshake when both partners issue the same greeting. The reply to How do you do? is How do you do? Then it would be a matter of getting straight down to the business in hand, e.g. ‘I see that your company has been performing very well in South East Asia...'

Answer 3

This answer offers only a broad picture without pretending to cover all the uses. This answer also provides another greeting and answers.

1) How are you?

Fine. And you?

This is the catch-all greeting, and in America you can use it with anyone from a social outcast to the president. When to use: the first time in a day that you see a friend, acquaintance or work associate. Definitely used if you have not seen someone for a day or two, for example: over the weekend. You also use it when approaching someone before making a request. This has the effect of breaking the ice before requesting something. In general, 'How are you?' is a ritual greeting more than an actual question. It has a sociological meaning something like 'I'm just checking if you are still alive.' However, some people might actually answer the greeting, which marks them as bothersome or, perhaps unaware that you aren't really asking them a question.

2) How are you doing? How's it going?

Great. How about you? Great! How's it going with you?

These are also greetings. But I myself usually preface them with 'Hello' or 'Hi' or 'Hey!'. In general, the first one can be used with someone you know, the second with someone you know or don't know. (The second one is also much less formal than 'How are you?') Having said all that, all three phrases mentioned so far can be actual questions. In fact, after using one as a greeting, you can repeat the same one at a real question.

3) How do you do?

How do I do what?

When to use: never.

Note: How do you do as a greeting or a question about someone's health, etc is rarely used in AmE these days. Thus, I might consider the literal words of the question, How do you do (that)? and answer like I did above. The answer is to indicate my attitude toward being asked a question that normal people stopped using long ago.

Bonus: the scene in the movie My fair lady with Audrey Hepburn when she goes to a horse race and asks haughty taughty people How do you do? is priceless.