I could calculate you could calculate he could calculate we could calculate you could calculate they could calculate
V-ing form
I could be calculating you could be calculating he could be calculating we could be calculating you could be calculating they could be calculating
Perfect
I could have calculated you could have calculated he could have calculated we could have calculated you could have calculated they could have calculated
V-ing perfect
I could have been calculating you could have been calculating he could have been calculating we could have been calculating you could have been calculating they could have been calculating
Negation
Simple form
I couldn't calculate you couldn't calculate he couldn't calculate we couldn't calculate you couldn't calculate they couldn't calculate
V-ing form
I couldn't be calculating you couldn't be calculating he couldn't be calculating we couldn't be calculating you couldn't be calculating they couldn't be calculating
Perfect
I couldn't have calculated you couldn't have calculated he couldn't have calculated we couldn't have calculated you couldn't have calculated they couldn't have calculated
V-ing perfect
I couldn't have been calculating you couldn't have been calculating he couldn't have been calculating we couldn't have been calculating you couldn't have been calculating they couldn't have been calculating
Interrogative form
Simple form
could I calculate? could you calculate? could he calculate? could we calculate? could you calculate? could they calculate?
V-ing form
could I be calculating? could you be calculating? could he be calculating? could we be calculating? could you be calculating? could they be calculating?
Perfect
could I have calculated? could you have calculated? could he have calculated? could we have calculated? could you have calculated? could they have calculated?
V-ing perfect
could I have been calculating? could you have been calculating? could he have been calculating? could we have been calculating? could you have been calculating? could they have been calculating?
Interro-negative form
Simple form
couldn't I calculate? couldn't you calculate? couldn't he calculate? couldn't we calculate? couldn't you calculate? couldn't they calculate?
V-ing form
couldn't I be calculating? couldn't you be calculating? couldn't he be calculating? couldn't we be calculating? couldn't you be calculating? couldn't they be calculating?
Perfect
couldn't I have calculated? couldn't you have calculated? couldn't he have calculated? couldn't we have calculated? couldn't you have calculated? couldn't they have calculated?
V-ing perfect
couldn't I have been calculating? couldn't you have been calculating? couldn't he have been calculating? couldn't we have been calculating? couldn't you have been calculating? couldn't they have been calculating?