When will the floss stop hurting

I do it once a day, which is what my dentist recommends. Usually at night so you don’t go to sleep with stuff in your teeth. Being gentle should prevent it from hurting.

I would suggest try different brands of floss. Some are shit, some too slippery etc etc. Also practice and improve your technique. Personally I found the Colgate floss to be too thick and Oral B is best suited for me.
Also fun fact : the gap between all your teeth may not be same. Some maybe a bit more bunched up, be careful on how much force you apply. Too much force and it'll go straight to your gums and you'll end up bleeding.
Last option if you are lazy is use a Waterpik or some other dental water flosser.
- Yeah, I’d say not cheaping out on floss is one of the more important things. I bought some cheap floss while on a trip since I forgot mine and it absolutely destroyed my gums even though I’ve been flossing for years without any issues.
  
  Yeah, I've been buying more expensive floss (Cocofloss) and it's awesome. God I'm old.
- Waterpik is not used to floss.
  
  Idk what you mean by this but both Waterpik and floss are interdental cleaners performing the same job. They have very subtle differences but ADA says either is fine as long as you’re doing one of them.
- It's Butlerweave or nothing for me!

This will tend to happen if you're snapping the floss in between each tooth. Use a gentle back and forth motion to slip it between teeth, and slide it against the side of each tooth gently. If it hurts, you're probably being too rough. Also maybe start with once per day, in the evening.

I’ve started flossing more times than I can count. You’re RIGHT on the cusp of it stopping hurting.
Some tips: — you don’t need to floss twice a day. — you shouldn’t be using a ton of force, but just do a quick swipe on each surface of the tooth under the gumline. — if you’re still bleeding heavily after 2 weeks consistently (like, mostly red spit after floasing rather than just having a little pink tint to the mostly clear spit), you may have a gum issue that needs a dentist to look into or prescribe a special toothpaste for. — try the “Plackers” brand of toothpick sticks.
Beat of luck!

Try a waterpik, or just go easier on yourself. Also grandma is right, flossing is really good for you and will improve your oral health a lot. I floss basically after every time I eat, it's just automatic and feels so good to have clean teeth
- Waterpiks are great but not really a substitute for flossing
  
  But they're a great substitute for not flossing, which is what I'd wager most people do
- Personally I advocate for having a beard - ready made floss is always at hand.

As a man with thirteen teeth, I wholeheartedly applaud your gran's tenacity. If your gums are damaged by not flossing, they'll bleed a lot at first.
Has your dentist recommended a deep cleaning? It's possible you have tarter under the gum line. That would cause inflammation and lead to more painful flossing. Once my gum disease was in check, they stopped bleeding from my water pick, before that, it was a fountain of gore.

Flossing shouldn't be painful. Maybe you're doing it wrong?
- Still painful for me after being consistent for 30 years.
  And yes, I do it right. I've had probably a dozen dentists.
  Not everyone is the same.

How are you flossing? I start at the back on the top, wriggle the floss in between my teeth, then bend the floss over one tooth and rub it up and down against the tooth down to the gum line. Then, I bend it over the other tooth and do the same. The goal is to clean the tooth right down to below the gum line. You want to get below the edge of the gum to clean the pocket around the base of the tooth. You don't want to injured the gum.
I started years ago when my doctor told me it would shorten my life if I didn't floss. Now I can't stand staring the day with unflossed teeth.
Take it easy on your gums. It will get better quickly.
- I was going to post this exactly. Stop hurting your gums OP!

If it hurts, you might be using a bit too much force
firm but gentle like cleaning the smugde off your phone is how I'd recommend visualizing it
too aggressive and you'll destroy your screen, too soft and you'll never get that smudge off
also like the other commentors have suggested maybe a waterpick could be another option you might want to try

Not a dentist. Should probably see one. Mine were in really bad shape. I didn't take care of them for a long time. I'm trying now. At first all the gums would bleed and hurt. A month later still bad. I ended up giving the gums a couple days to heal every once and a while then back to once a day. Two years later still two spots that hurt a little and bleed some times. It can take time, dont get discouraged. I think its something that if you don't do, its hard to get back to healthy. Keep in there, don't give up. My teeth are a million times better than they were.

your gums are fucked you need to go to an ass doctor

Important question: are you bleeding from the gums when you floss?
Healthy gums can handle normal flossing without bleeding. I floss once a day, before bed. Normal flossing does not involve super hard scrubbing, just enough force to scrape off stuff stuck between the teeth and dislodge stuck particles. You might also want to add some antiseptic mouthwash to your routine after flossing until your gums stop bleeding.
- After 30 years of being a consistent flosser, and trying everything under the sun, mine still bleed. Multiple dentists in that time have determined gums are healthy.
  
  That's frustrating, sorry to hear that.

I use water floss and interdental brushes. Not sure if that will make a difference in your case.
Best to talk to your dentist.
- Listen to this guy/girl OP.
  Your dentist will almost certainly recommend:
  -Getting an electric toothbrush, READING THE INSTRUCTIONS, and using at least twice daily.
  -Simultaneously, getting a water-pik or similar (they make travel ones too) and using it twice a day. (Tastier if you fill it with mouthwash).
  Or shell out ~$10k or more (in the US) later for ignoring this advice, like I will in April, for gum restoration procedures.
  Plus nobody will tell you you have eye-watering bad breath, but they will certainly hold it against you.
  
  Proper mouthwash is a game changer.
  Had problems in my 20's (30 years ago), old dentist: "use mouthwash 2-3x a day, and not that newfangled nonsense, I mean Listerine. Yea, it tastes awful, but it works." hahaha
  Dammit if he wasn't right about my issues at the time.
  And modern electric toothbrushes are a game changer. Not like the truly electric (as in you plug it in) when I was a kid. I think improved brush heads and especially the built-in timer make the difference.

If you’ve never flossed before this could take a while to adjust to. Basically you have to heal and strengthen. If you haven’t been in s as long time, be sure to have a checkup with your dentist.

Twice a day is way too much. Maybe 3 times a week, or less if you're trying to actually get started and improve the health.
Also, they make little interdental brushes in various sizes that can be much less aggressive when your gums are still very sensitive and inflamed. You should be able to find them at the dental section of your supermarket.
It'll take a few weeks for your gums to toughen up. Then you can go crazy on the floss if you want.

Yes, however part of it is technique: Flossing will probably always hurt if you are just sawing into your gums with string all the time. The idea is to use it to clear stuff off your teeth, so try to get the floss to conform to the curves of your teeth as best you can. If you're using flossers, consider switching to regular string. They also sell flossing toothbrushes.
However you floss, try to keep it up along with regular brushing using fluoride toothpaste before bed. I brush when I wake up too.
- Great advice. I've been using flossers lately because of a broken shoulder, and I can definitely tell that the quality of my flossing is lower than it is with regular floss. It's also harder to be gentle.
  
  Yeah, flossers are kind of more of an in-a-pinch solution IMO. You might try a flossing toothbrush too, hope your shoulder heals soon!

In addition to what everyone else is saying, use a wider tape floss. The narrow string ones tend to sting a bit. Source: me, bought a big roll of the cheaper string type and cat wait to be done with it.
- I second this, the wider ones are so much more comfortable to use and do a great job.

dance or "dental care"?
- This one took me a sec (because I'm old) but then I chuckled heartily (because I'm old)
  
  username checks out
- Could also be computer programs....

Once a day is good for flossing, I do it just before brushing my teeth at night, so the bristles and toothpaste can get where the floss cleared out the gunk. It should stop hurting soon and just "wake up" your gums instead.
Think of the floss like a blade and scrape, don't saw! Obviously if your teeth are tight together you might have to wiggle back and forth a little to get between them, but as soon as you get down to your gums, only go up and down, scraping the side of each tooth, not really going after the gum itself.
I like the Oral B GLIDE "gum care" flossers, because you can pinch to pull the floss taut and wiggle it between tight teeth, then relax it to curve around the sides of the tooth, and get the correct angle even way at the back of the mouth. I rinse and reuse them several times for less waste. Otherwise I like Floss Tape, which is wider than regular floss for more cleaning, less cutting. It'll also braid into a stronger rope for escaping from prison or rescuing princes or whatever.
Try swishing with warm salt water when your gums feel sore, you can do it anytime. And get some extra vitamin C into your system. It's good for gums, that's why bad gums are a symptom of scurvy.
Good on you for doing what your grandmother says! At our age, we know how important it is to keep your teeth as healthy as you can, and as long as you can.

Never.
At least it never has for me, and I'm probably old enough to be your grandfather.
I've tried everything - desensitizing toothpastes/mouthwash (though I wouldn't expect those to help with flossing pain), salt water rinses, every type/brand of floss.
So yea, don't believe everything medical professionals tell you about how things "should" happen. The operative word there is "should". As in "usually", or "most often".
Everyone is different, so not everything will work the same for everyone. (I can go through a laundry list of meds that work/don't work/negative side effects/no side effects for individuals in my family. The variability is astounding among a group of genetically similar people).
Best you can do is be consistent with your flossing, find the right type for you (I find the waxed tape style the best for me), brush at least 2x/day (preferably 4x), use the right brush style (generally as soft as will work), replace it regularly, and I found using a modern electric toothbrush helps tremendously (especially the Phillips Sonicare, they have some actual studies behind their efficacy). After going through a few different toothbrushes, the Philips is so effective for me that my annual cleanings have gone from sucking to being a breeze.
- Why are you being downvoted? "Never" is the correct answer.

In my experience you should consider yourself successful if there is no bleeding. It never ceases being painful.

it will go away eventually