Rhyming Couplets in Iambic Pentameter
The content of this poem is hard to wrap your mind around, so fortunately the form is standard English Renaissance stuff. The poem consists of five rhyming couplets: yesterday/away, past/last, two/do, you/too and I/die. You can see that lines 5-6 also rhyme with lines 7-8, but they are still considered couplets. Also, be careful: this one is only ten lines long, so it's not a sonnet. Sorry, sonnet lovers. You'll have to check out some of Donne's other amazing work, like Holy Sonnet 7, Holy Sonnet 10, or Holy Sonnet 14 to find your fourteen-lined friend.
"The Computation" begins with an interesting rhythm:
For my first twen-ty years
These first six syllables contain two anapests. An anapest is two short beats followed by a long, accented beat (da-da-DUM).
As for the remainder of the poem, the meter is all over the place, but the closest we can approximate is iambic pentameter, which is a ten-syllable line with five iambs, or short beats followed by long ones (da-DUM). Here's a perfect iambic pentameter line:
For for-ty more I fed on fa-vours past
But Donne bends the normal rules of time out of shape in this poem, so why shouldn't he bend the rules of meter, too?