How long can you stay on a 1200-1400 calorie diet?

I've been eating between 1200 and 1500 on most days since early January, with occasional exceptions (such as this weekend). During this time, my cholesterol profile improved. I recently had kidney, liver and metabolic panel tests which were completely normal.

Choose a calorie deficit that is safe and works with your body and your needs.

I have been on 1200 calories since Nov.15, 2014. Almost 5 months. I have lost 60 pounds and am feeling great. I had blood work done in early November that came back alarming. Pre-diabetes, low iron, low vit d, low b12, thyroid screwed up. I started this journey the next day and would not change a thing. I had my blood work repeated in February and my A1C was back to normal, my vitamins were back on track and they actually needed to lower my thyroid medication!
I eat back half of my exercise calories and drink at least 10 cups of water each day. Life is good and getting better and better each day!

15 minutes

6 and a half months so far. Lost about 65lbs. Eat high protein and do cardio and weight training 4-5 times a week. No noticeable muscle loss. Started at 240lbs, now 175lbs and wearing size 10 and some 8's. I'm 5'8" and 47 years old. I was at 1200 for 5 months and recently switch to 1450 (although I don't reach that number all the time). I wanted to eat more fruit and nuts so I upped my calories. There are days I still come in at 1200 (mostly on weekends when I wake up later than normal). I don't eat back exercise calories and really "spend" my calories wisely. Candy and sweets are what got me into trouble so I stay away from them and choose fruit and tea to satisfy my sweet tooth. Feeling better than I have in years. Always take the stairs, drink lots of water and training myself to not live to eat. I love cooking and creating less calorie dense meals that I can enjoy and feel satisfied. I think it depends on what you eat. Some folks want desserts or the occasional pizza so 1200 calories won't work under those circumstances, I don't think. I'd be starving if I didn't spread my calories with high protein and lower cal options like egg whites, tofu, chicken breast, greek yogurt, etc. But I also eat whole eggs, cheese, olives, oil, etc.

Everyone is different. Some can handle it and some can't or won't. I haven't suffered a day since I've started losing weight. In fact, on my vacation I ate some higher cal options and felt like crap. When I get closer to maintenance (around 140-150lbs) I may allow for an occasional night out with friends but I've changed my lifestyle for good.

I didn't know that it could be dangerous to eat just 1200 calories. I've been averaging between 1100-1300, but I'm short and I need to lose probably around 90lbs total. Does that make a difference?

Six hours, because that's just breakfast and lunch.

I did 1200 for about three years. Lately I've been aiming for 1300-1400.

I don't find it difficult at all. You can certainly get decent nutrition on that many calories.

I eat ~1200. However, that doesn't include exercise calories. I walk 3-5 miles every day and just started adding in a few blogilates videos every other day. I eat back between .5 and all of my exercise calories---just recently cut back to half, because I lost enough to stop losing on eating all of them. Basically, I exercise to eat more. I've been doing it since November. My health is so much better now. I'm also short, otherwise sedentary, and a 35 year old woman. My actual calories eaten is usually around 1330-1400. I don't sweat it if I go over a little, because it prevents binges. My macros need a ton of work, though...that's my next thing to work on, after adding in the blogilates more regularly.

It really depends.
I'm extremely short (4'10)
So eating 1200 calories hasn't been an issue for me.
I've been doing this for going on 8 months now and I'm down 17+ pounds.
I haven't had any bad side effects, or anything of that sort.
But I do give myself cheat days once to twice a week and allow myself to eat pretty much what I want within my calorie limit.
The lowest I go is 1100 calories, when I'm not exercising at all in the day. But I don't do that very often, it usually just ends up happening.

I lost 20 pounds over about 6 months eating at 1300, I have since gone up to 1500 and am still losing, now at about .25-.5 pounds per week, which is appropriate for me as I am approaching maintenance and I'm not even clear how much more I really want to lose. (5'6", 45 years old)