How does the script behind fluency work?

I began the spanish from english tree about 6 weeks ago and skipped the basics by doing the placement test as I have been studying spanish for the last 5 years in junior high and high school. This got me placed at level 9 with a 30% fluency rating from day one. However Duolingo's perception of my spanish fluency has since somehow declined significantly to 13% although I have managed to keep a so far 33 day streak and I have leveled up from level 9 to level 11. This feels very weird to me. If someone can explain how the fluency percentage work it would be very much appreciated.

March 13, 2016


fluency = rand();

March 13, 2016

It would be awesome if a new algorithm was implemented as the current method seems completely inaccurate. I feel like the word count should have some bearing on one's fluency.

June 14, 2016

I have to admit, that's pretty funny.

March 13, 2016

This is from the duolingo Help Center

Fluency measures your mastery of the vocabulary and grammar of a language and your ability to understand and produce the language.

Duolingo estimates your fluency based on your progress through the skill tree and the accuracy of your answers. Because learning a language requires repetition, we also take into account how regularly you practice. Without continued practice, your fluency score will decline, based on our model of how the human brain forgets over time.

With Duolingo, you can achieve a fluency as high as 50-60%, which is equivalent to Advanced proficiency.

That sounds like a big drop from 30% to 13% though, I don't know what's going on. Most people seem to think it's best to ignore the fluency percent because of it's flaws and randomness.

March 13, 2016

Why have the fluency percentage if it doesn't mean anything?

April 19, 2017

thanks that explains it. I have been practicing Spanish for 53 days and have been hovering around 57-58%, in fact yesterday it was 58%. Today it shows 50% which is discouraging.

April 19, 2017

I can feel your pain. I have been practicing Spanish for three years with a fluency of 56–57%. This Monday my fluency dropped to 52%. It is very discouraging.

April 20, 2017

I am on day 114 and have not missed a day. I study for two to three hours and my fluency has gone from 31% to 26% and dropping. I was trying to do a new topic each day but think that has hurt me. Thinking I need to concentrate on what I've done so far and not take on any new subjects until my fluency goes up? Would appreciate feedback fro duolingo.

May 26, 2017

Are you practicing on the website or on an app? Anecdotally, the app seems not to credit your work to your account properly.

If you're rushing through a skill a day, it seems likely that many of your skills degild at more or less the same time. I don't know for sure, but would not be surprised if that does cause your fluency to be lower, especially if you're having trouble keeping on top of regilding.

The fluency metric is widely believed to be inaccurate, however, so I recommend not taking it too seriously. I certainly wouldn't use it as the basis for making decisions about how to practice.

May 28, 2017

From my experience, the website and the app certainly measure it differently. My French fluency stayed at 9% for weeks on the mobile app, but after 30 mins on the website it suddenly jumped to 25%. I think the website is being too generous in my case, though. :-)

June 24, 2017

In regards to the question raised of what the algorithm is behind the fluency parameter.

It would be nice if the algorithm behind the fluency parameter could be revealed. Somehow you want such parameters to maybe modify and improve your learning. Based on my experience I can only conclude that the fluency calculating algorithm is different for each language you learn. It could very well be that it is also influenced by one’s own approach in going through the tree. I have twice the XP in Spanish, in other words I learned it 3 month longer than French. Yet my fluency is stuck at 29% with 2536 words while my French fluency constantly moves up now to 41 % with only 2126. To top it my French tree turns very fast totally grey while my Spanish mostly stays yellow. To some extend I would even like to know the total average time spent on each XP in different languages.

I thought I could conclude that French is easier for me than Spanish> Maybe it must have to do something with verbs in Spanish being totally complete. It could also be that with knowing English, German and now Spanish my guesswork is better in French. However, the strange tree behavior lets me hold off. I also noticed that with the upgrade the French tree is much bigger.

I am native in German as well. I just have not used it much for 30 years and noticed that my ability to switch easily in complex topics decreased. I even used Google translate and then improved on it to write German messages. However, I am grateful to Duo for giving me this option, since my German hang-ups as confirmed by friends -- even discussing now very complex topics have totally disappeared. My German fluency is now 61 % with only 1642 words. The other reason I am doing German is that I have Kids who did not grow up in Germany. They speak French and English as well, but the German fluency lucks. I was working on trying to relate presented Duo German Grammar concepts to patterns presented in to the Duo Tree. I think both Duo and I are when it comes to that on a learning curve.

I can totally accept that Duo puts the bar at 60, since there are disadvantages with the Duo more translation based learning approach over an immersion approach

July 3, 2017

My fluency has dropped slowly from around 50% to 42% (as of today's last check) during that past couple of months even though I've nearly completed the second German tree.

My mind tells me not to worry about the fluency meter, that my comprehension of the vocabulary and grammar are most important, but my heart still cries out when I see that stupid meter decrease point by point. It's mildly infuriating.

April 15, 2016

2nd German tree? I only see 1 so far.

June 16, 2016

This is the second version of the German tree. There was one before it that was not as robust. They changed it about the time of my post above, which says 2 months ago. Hmm, feels like it was longer than just two months though.

June 16, 2016

I am on a 94 day streak, am getting the odd question wrong (usually the very poor audio) and was happy with my 50% fluency in French. But when I woke up next morning it had dropped to 49% before I embarked on the days revision!! Why is this duo? I need to sleep!!

April 22, 2016

Are you using the app or the website? I hear that practice done using the app is at least sometimes not counted towards the fluency percentage.

March 13, 2016

Maybe this is my problem. I NEVER use the website, only the app. And my fluency is steadily decreasing. I was actually surprised by some of the tips available on the website just now. I've been using only the app for about two years now. My fluency had gone up to 50, but is steadily decreasing over time.

EDIT: For the least five days I've been using the website and not the Android app, and my fluency score increased from 46-62%. Apparently the app is not working for fluency.

April 16, 2017

I only use the website, and my fluency rating has dropped from 54% (what I got for testing out of the tree first try) to 43% despite spending the past few weeks concentrating on re-completing the tree to get everything gold again.

I've "practiced" tons the past few weeks, my entire tree is gold, including the bonus skills, and I'm still at 43%. It's not only frustrating; it's insulting.

April 25, 2017

Once again I went to bed 50% fluent in French and woke up 49%. I will be fascinated to learn what "algorithm" is driving this oddity Duo, Does a native Frenchman lose fluency overnight? As of now I have absolutely no modules understrength so I am looking forward with interest to tomorrows score! I know that the % itself isn't of much consequence but it is the "science" of the thing that is interesting me!

April 23, 2016

I think it's kinda messed up. I'm apparently 52% fluent in Spanish, which seems fair enough since I've been learning it for 9 years (initial placement test put me at level 9 with 50% fluency). In Turkish I'm 0% fluent, which I thought was okay since I've only done the first few lessons, but then with German I went from 3% to 11% fluent by doing one test on grammatical gender after not having practised for a week??? (at the time of writing I'm level 7 in Turkish, but only level 3 in German)

May 4, 2016

It's very messed up. It says I'm 29% fluent in Portuguese, and I haven't even completed 25% of the tree, but Spanish, in which I'm fluent and have the ENTIRE tree in gold (including bonus skills), I'm only 43%.

(My initial placement put me at 54% fluent. I'd have thought after practicing enough to turn it all gold again I could at least get back up to 54%, but nope.)

An even bigger laugh is my 22% fluency rating for Swedish, for which I've only done 5 lessons total, two of which have "faded" severely. Yet somehow duolingo thinks I'm more than half as fluent in Swedish as I am in Spanish.

Very messed up.

April 25, 2017

I don't know what system they use, but it is really odd. I finished the Italian course, practice daily and had everything gold a few days ago(about a third are now at 4/5) and am at 19%. I started the French course a few weeks ago, also practice daily, but only have about a third done and am at 35%. Very strange. Maybe it is an inverse scale? :-)

September 2, 2016

I am still wondering about the algorithms Duo. Yesterday my fluency dropped to 49 and it was still 49% this morning. Then I did a simple "strengthen" and made several silly mistakes because I wasn't concentrating and yet my score rose to 50% again!! Bizarre!

April 25, 2016

Did you switch from the website to the app? I read elsewhere that the app doesn't count all the words and that people who go from the app to the website may double their fluency scores in only a couple of days.

April 30, 2016

No I don't think so although I do use both. I was rather hoping that someone from Duo would respond. After all it is their system.

April 30, 2016

I've been using only the website and my score has been dropping despite the fact I AM fluent--and was before starting duolingo--and I have the entire tree in gold.

April 25, 2017

I'm very curious about this as well, since I got up to 40% fluency in Spanish today, and through the course of the day- despite practicing all day- it's dropped back to 39%. Something has to be going on with it. And I know people say its the levels that really matter not the fluency percent, but I use the fluency to link onto my Linkedin profile.

July 6, 2016

I love the potential for this "fluency meter" - it's fun to watch - but clearly it STILL doesn't function as it should. Duolingo needs to find a decent algorithm for this if it's going to be useful in any way.

April 4, 2017

It would be very good to get some explanation from Duolingo as to how the fluency rating works. After reading some of the comments in this thread, it does seem to not work very well.

In my case, I have been stuck on 71% for weeks. I have consistently done over 100 xp per day during that time, but the fluency rating does not move. It is indeed frustrating. I know I am not perfect in German, but it does seem that it should respond in some way.

January 29, 2018

A "Duolingo Fluency" of 71% is one of the highest scores I have ever seen in German.

More information about Duolingo's "Fluency" in

Keep in mind:

  • Duolingo's fluency % is a nonsense number.
    It says nothing about your fluency in the real world.

  • Duolingo's Fluency % is unreliable.
    Recently appeared that the Duolingo staff had manipulated this "fluency %" for testing purposes (

In the comments of this discussion you can read some tips to improve your German

However, I think Duolingo's courses are excellent.
Just enjoy the courses and don't worry about Duolingo's fluency %.

January 30, 2018

Don't worry too much about the fluency. Sometimes it's not accurate, and it really doesn't help. The thing to really work for is leveling up. People can see that and it's the only thing that can tell them about how much you have completed the course.

April 10, 2016

Actually (as has often been pointed out on this site) you can reach level 25 by doing lesson 1 over and over (and over and over) again. Obviously, no one recommends this, but the correlation between level and progress down the tree is indirect.

April 12, 2016

Yeah but level isn't accurate either since it's based on practice. I am actually fluent in Spanish and knocked off the whole tree in a day just by testing out of stuff (I was bored), but my level is only 11 - and will never get any higher since I have no need to practice Spanish.

November 9, 2016

I do mostly timed practices and I never use the phone app. Every day I earn about 150 XP with timed practices and so far my fluency is staying at 50% in Italian. Maybe the timed practices help to maintain the % better than the untimed ones ... this is conjecture but it might be worth giving it a try. Good luck !

May 11, 2016

My experience states otherwise. I've been doing the timed ones because they help turn the parts of the tree gold faster and I wanted to get my entire Spanish tree gold again. Finally got it all gold, and I'm still way down at 43% (down from an initial 54% that I got from testing out of the tree the first time).

April 25, 2017

i admit it s kind of frustrating ... been working on my swedisg 18 days in a row, doing like 1h exercice a day. my fluency stays is at 2% even if i did 18 complete lessons and i m at level 9 . My friend just started duolingo spanish and got 2% in 1 day by training 2 lessons ( basics ) . i keep on working because i feel i learn everyday new stuffs , and obviously because i want to be able to speak soon but it s not really rewarding somehow...

February 1, 2017

I've just read all the comments below, and found it very helpful to know lots of others are as confused and frustrated as I am. I've been practicing Spanish daily for over a year, about 20-30XP a day, and very regularly for about six months before that. My tree has been completely gold for the past year.

My fluency was at 69% for many months, then suddenly about two months ago it dropped to 53% with no explanation. Since then it's been slowly trending downward - now it's at 49%. I'm practicing the same amount, in the same way, with about the same accuracy. I know my Spanish is improving, because it's getting easier and easier to speak with others, and my reading and movie-watching comprehension are getting better.

So weird. As a number of folks have said below - why even have fluency % if it's so random? It's demoralizing!

June 9, 2017

Had to come and tell my version here too, since I find this interesting, perhaps even a broken feature. Back in school I used to study Swedish for seven years as a compulsory subject, plus some courses at the university. I wasn't very motivated though and never learned to cope with it in any actual situations.

With this background I started Swedish on Duolingo last week. First I tried the replacement test, which forced me to start right from the beginning. Then I started going through the individual lessons quickly by testing them out. Only had I reached the last part of the tree did I actually go through them ad paid more attention. Now my tree is done I just maintain it golden while looking for other methods to brush up.

All this time my fluency according to Duolingo has remained at 2%. Yet I seem to be able to have conversations with my Swedish-speaking friends on various subjects and mostly understand newspaper articles. Perhaps the number will rise in time if I just maintain my tree golden? Or can it really have got stuck?

June 24, 2017


August 21, 2017
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