On bed

[tufguy]

If DR says that I have to take bed rest for eight months, so can I say "I have will be on bed for next eight months" or "I have been on bed for eight months" or after eight months "I was on bed for eight months"?

 

[bhaisahab]

"I will be in bed for the next eight months." Future. You are not yet in bed.
"I have been in bed for the last eight months." You are still in bed and you have been there for eight months.
"I was in bed for eight months." Past. You are no longer in bed.

 

[emsr2d2]

You need to understand the difference between "in bed" and "on a/the bed".

I am in bed = I am lying down, probably under a sheet/duvet, with my head on a pillow and I'm either resting, trying to go to sleep or I've just woken up.
I am [lying] on a/the bed = I am in a horizontal position on a bed. There is no specific suggestion of sleep and I am probably lying on top of the sheet/duvet. It simply indicates where I am.

 

[Skrej]

You could also use the adjective 'bedridden', which means confined to bed due to infirmity.

"I was/will be/have been bedridden for 8 months."

 

[Barb_D]

In the US, you'd say "on bed rest" to mean that you are confined to bed by doctor's orders.

 

[Tdol]

If it's on doctor's orders, you could also say that you were/have been,etc, confined to bed for eight months.