As with many things in life, how long it takes you to get a doctorate degree depends mostly on you.
But if you are disciplined and you work hard, how long should you expect it to take to get a PhD?
In The UK
In the UK the huge majority of PhD candidates will begin a PhD after completing a relevant masters course. A masters degree will usually take around one year to complete if you are studying full time, or two to five years if you are studying part time. Once you've gained this qualification you can then move onto the doctorate. In the UK it usually takes three to four years of full-time study to gain a PhD, including a year of writing up your thesis. So from undergraduate to doctorate, you should expect it to take at least four years full time. Not many PhD students undertake their doctorate on a part-time basis, but those who do will have between five and six years to complete their PhD. The whole process is done on a part-time basis would take seven to 10 years, depending on how much time the student is able to commit to it. There are some doctorate degrees, like the Doctorate of Theology and Practice at the University of Winchester, which are studied by distance learning online. These tend to be part-time only and usually take up to seven years to complete.
Different countries in Europe have different traditions and regulations surrounding doctorate degrees. Most countries are similar to the UK, where you complete your PhD once you have done a relevant masters course. For example, in Germany it depends on the subject of the PhD as a scientific subject might take two to three years full time, and a doctorate in the arts or humanities may take between four to six years full time. Part-time PhDs are unusual in Germany but you could expect this to take four to eight years. France is similar to Germany, and it takes around three to four years for a full-time doctorate in the sciences, and four to five years for a doctorate degree in the arts and humanities. In Norway, all PhDs usually take three years on a full-time basis – here is a great explanation from the University of Oslo. It can take up to six years to complete a PhD on a part-time basis, but this way of studying is unusual.
In The USA
The USA has a different university set up to the UK and Europe as most doctorate degrees are gained by going to Graduate School straight after you have completed your undergraduate degree. This means that the time it takes to gain your masters level qualification is built into the time it takes to get your PhD. It is common for it to take four to five years to gain a Doctorate from the time you start Graduate School, but it can take up to eight years of full-time study. It depends on the institution and the type of PhD you are going for. Some institutions, like Franklin University, allow students to transfer credits and count professional work experience towards their doctorate degrees, so you could complete a PhD in as little as three years. Part-time and online PhDs are more common in the USA and these take anywhere from five to 10 years to complete.