I can't understand: what's the difference between complicated and complex?

They seem to be used interchangeably. Are they actually different at all?

  • 18
    ...it's complicated. Or do I mean complex?
    – Matt Ball
    Jan 28, 2011 at 19:44
  • Read this larrycuban.wordpress.com/2010/06/08/…
    – user16914
    Jan 11, 2012 at 15:22
  • 2
    In system theory: a system can be very complicated but not complex at all. Is system is complex when it has emergent behaviour. Complicated systems can be solved with enough computing power. Complex systems cannot be solved. thegreatcourses.com/courses/understanding-complexity.html Mar 13, 2015 at 23:51
  • 1
    Complex means a system which is elegant, reasonable and beautiful but takes time to learn and comprehend. Complicated means a system which is ugly and cobbled together without any explainable justification other than 'it seems to work'.
    – raindrop
    Dec 1, 2018 at 16:29
  • This is weird. 9 years after this question was asked, and it still seems that there is no concensus as to which is which. Different people use these same words with completely opposite meaning. I lean towards the meaning of complex = solvable; complicated = not solvable. But, for example, the larrycuban article linked to by @user16914 uses them completely opposite to that! So, too, does a poll of these answers here. So what is it? is this to complicated to answer?
    – JDS
    Jun 5, 2020 at 15:21

11 Answers 11


Complex is used to refer to the level of components in a system. If a problem is complex, it means that it has many components. Complexity does not evoke difficulty.

On the other hand, complicated refers to a high level of difficulty. If a problem is complicated, there might be or might not be many parts but it will certainly take a lot of hard work to solve.

  • 24
    This is not correct from a mathematical perspective. Complicated problems or systems are 'large' but still solvable or deterministic. Complex problems or systems have emergent properties and behaviour (such as self-organisation) that makes them non-deterministic / non-solvable, regardless the amount of computing power available. Very simple systems can also be complex. Very complicated systems don't need to be complex. These is a good primer on complexity. ncbi.nlm.nih.gov/pmc/articles/PMC2465602 Mar 2, 2017 at 12:20
  • 2
    Could you add a few examples of things which are "complex but not complicated" and "complicated but not complex"? I think this would helped enormously to understand the difference between the two terms. And also add the opposites for both the terms. Oct 29, 2021 at 19:52
  • If my memory serves me right then during my time studying Petri nets, complexity referred to the level of how unpredictable a system was while its "complicatedness" related more to its intricacy. A single product line consisting of 3 robots is not very complicated nor complex. Swap one of the robots out with a human, and the system is equally (non) complicated but much more complex because the human is much less predictable than the robot. An analog wrist watch, on the other hand (pun intended), is very complicated with all its moving parts, but is very predictable and hence not complex. Nov 18, 2021 at 14:12
  • 2
    Could be correct for "mathematical perspective". In fact, complex numbers are called that because they have two components.
    – GEdgar
    Mar 11, 2022 at 1:35

I am forced by my nature to add a more pedantic answer to the list. The content of this answer does not reflect my personal opinion, nor does it reflect common usage, but it does explain why the two words are not precisely interchangeable in all circumstances.

Complexity is intrinsic. Something is complex if it involves a lot of [metaphorical] moving parts even when considered as a Platonic ideal.

Complication is extrinsic. Something is complicated by external influences, or because of external influences.

Pedantically, something can be complex without being complicated, or complex because it is complicated. (Things are rarely complicated without also being complex.) In realms where precision is important, there is often a distinct division between the terms. In medicine, for instance, a broken bone may be described as a complex fracture because the fracture is complicated by breaking the skin, inviting the risk of infection.

Here endeth the pedantry.

In common use, complex is more usually used in a technical sense. Complicated is more likely to appear in everyday language among the general population since most complexity in everyday life is complicated in some way. Complicated may not always be precisely correct, but most people don't spend their lives with a dictionary in one hand and a thesaurus in the other looking for le seul mot juste -- they already have a word that means what they want to say.

  • 4
    Though I perfectly understand that all these simple "thanks" comments are The Wrong Thing on this site -- I am forced by my nature to write that I personally think that this is a great answer, and I am really grateful for this wonderful explanation ) Feb 17, 2013 at 14:37
  • 1
    I see. So, according to your pedantic explanation, the original verb meaning is implicit in the participle "complicated". A problem is complicated (adjective) because some external factor has complicated (verb) it.
    – Cameron
    Dec 8, 2016 at 4:45
  • Hey @bye there is no chat system for stackexchange, but I just wanted to say I've read through a lot of your answers to different questions on the word usage in English and I think they're really great. Thanks for sharing!
    – zachaysan
    Mar 8, 2018 at 15:25
  • Could you add a few examples of things which are "complex but not complicated" and "complicated but not complex"? I think this would helped enormously to understand the difference between the two terms. And also add the opposites for both the terms. Oct 29, 2021 at 19:52

In the Zen of Python, we have an aphorism

Simple is better than complex.
Complex is better than complicated.

It's a handy guideline when you are designing something.

  • 4
    This was actually (partly) what led me here.
    – erb
    Jun 5, 2014 at 12:21
  • 11
    How does this answer the question? Just says "oh complex is better, use that if something is complicated but it's not that bad."
    – user36720
    Aug 31, 2014 at 2:25
  • 5
    Sorry, it does not answer the question. Just gives another data point on usage. Aug 31, 2014 at 2:57
  • 10
    So when programming python, you can divide up a task or problem into separate parts. The more parts, the more complex. Simple is better than complex, so don't add too many parts if you don't need them. On the other hand, if you want to do everything in one part, it might end up being too difficult, too complicated. Making it more complex (more parts) is better in that case. Dec 21, 2015 at 10:59
  • 1
    @ReinoutvanRees "If your application is getting too complex, add more classes" - Object Solutions, Grady Booch. But he should have said "complicated", not "complex" :-) Jan 19, 2021 at 20:45

One subtle distinction between the two is that where the complexity was in some sense introduced, it is probably more common to use "complicated" than "complex." For example,

The instructions were way too complicated.

It is of course true that the instructions were also complex, but the silent implication in using "complicated," the past participle of "to complicate," is that somebody caused the complexity, as opposed to it being inherent in the subject. As a result, "complicated" sometimes has a negative connotation, effectively meaning "unnecessarily complex."

Quantum mechanics is an inherently complex subject, but the textbook was an even tougher slog because of the author's complicated explanations.

However, as others have said, there is a large overlap in the use of the two words.

Also, the idiomatic retort "It's complicated" is a sort of defense or apology for not being able to give a simple, and often expected, answer:

"What were you doing with Teresa? Don't you love your wife?"

"Yes, but ... it's complicated."


These words have a really large overlap, but they each have some distinct uses.

Complicated can refer to things that are difficult to explain because they are unclear rather than because they have a lot of parts. For example, Facebook's "It's complicated" relationship status could refer to a relationship that is one-to-one, but not well-defined.

Complex also has some technical meanings, as in "Complexity theory". This is related to the idea that the behavior of a system cannot be fully understood even if the parts are understood. This meaning is much more specific than what is conveyed by "complicated".

  • 1
    Math is complex, Facebook UI is complicated.
    – john c. j.
    Oct 1, 2020 at 0:08

You can use them interchangeably.

Complicated: consisting of a lot of different parts or details and therefore difficult to understand. Examples:

1- The rules of the game seemed very complicated.

2- I didn’t realize programming the VCR would be so complicated.

3- The brain is like a very powerful, very complicated computer.

4- a complicated issue

Complex: a complex process, relationship etc is difficult to understand because it has a lot of parts that are all connected in different ways. Examples:

1- The chemical processes involved are extremely complex.

2- the complex relationship between government and the media


As reported by the NOAD, the meaning of those words are:

complicated /ˈkɑmpləˌkeɪdɪd/
1. consisting of many interconnecting parts or elements; intricate: a complicated stereo system.
• involving many different and confusing aspects: a long and complicated saga.
2. Medicine involving complications: complicated appendicitis.

adjective /ˌkɑmˈplɛks/
1. consisting of many different and connected parts: a complex network of water channels.
• not easy to analyze or understand; complicated or intricate: a complex personality, the situation is more complex than it appears.
2. Mathematics denoting or involving numbers or quantities containing both a real and an imaginary part.
3. Chemistry denoting an ion or molecule in which one or more groups are linked to a metal atom by coordinate bonds.

The meaning of complex partially overlaps the meaning of complicated; the difference is that complex is also used as noun, and in specific contexts with a specific meaning (see Chemistry, and Mathematics).


Complex is generally used in technical situations, where a problem has a lot of components and aspects.

Complicated is more used in social situations.

Of course, you could say that "I am in a relationship and it is complex" and "This project's architecture is complicated". It would not be wrong, but it sounds a bit off to the ear.

The usage of these terms is different, that's all.

  • 1
    I actually have to say that the usage in your example sounds much more logical to me than it would sound the other way round. In fact, scientifically speaking there are few things more complex than human social interactions. But I agree that the colloquial usage would be the other way round. Jan 28, 2011 at 18:35

There can be no better explanation than in this TED talk by Eric Berlow (only three minutes, so go watch it!).

To quote the salient bit:

A well-crafted baguette fresh out of the oven is complex. But a curry/onion/green olive/poppy/cheese bread is complicated.

(That said, I actually disagree with Eric Berlow on the topic of network complexity. I’m a bioinformatician, we deal with complex interaction networks (mainly of the cell), and let me tell you: are they ever complicated. It’s safe to say that we (the scientists) understand almost nothing about these networks and reducing or interpreting these complex networks like Eric Berlow does in his talk is simply not possible. I suspect that this talk is more show than anything else.)

  • The quoted sentence is hardly an explanation of anything. Which characteristics of these kinds of breads make some of them complex and others complicated? Even assuming that the distinction can be clearly articulated, does it reflect how these terms are used generally or only how they are used within that talk?
    – jsw29
    Mar 11, 2022 at 17:37

In a nutshell:

  • complex is the opposite of simple;
  • complicated is the opposite of easy.

For instance, a smartphone is a complex technology but it is not complicated to use. Conversely, chess is a not a complex game but it is complicated to master.

  • 1
    Your answer could be improved with additional supporting information. Please edit to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center.
    – Community Bot
    Mar 10, 2022 at 22:39

In the context of their use as an adjective in practice, the truth is that there is no clear distinction between the two terms.

There are a few contexts in which one is more idiomatic than the other. For example, while I don’t use Facebook anymore, I recall a dropdown menu for relationship status including an option for “it’s complicated.” At least in American English, “it’s complex” would be somewhat unidiomatic, although people would get your meaning, and hardly anyone would even pause, let alone correct you.

Some answers here indicate that one of the terms refers to the abundance of constituent parts, whereas the other refers to a level of difficulty inherent in understanding the subject. However, if you look at a dictionary definition, you will often find both definitions listed, and/or one word defined using the other. Here’s a screenshot of the Google search result for “complex definition” which demonstrates both, which is attributed to Oxford Languages: screenshot of definition

Furthermore, any system with a sufficient number of constituent parts will also be inherently difficult to understand, so in a sense the two definitions are practically synonymous.

I contend that there is no correct answer to this question which provides clear separation between the two terms.

Unless you encounter both terms in a single technical document, and that document provides a glossary which clarifies the intended definitions, you would do well to treat them as synonyms.

Not the answer you're looking for? Browse other questions tagged or ask your own question.