wǒ wánquán dǒng le.

I

Breakdown of wǒ wánquán dǒng le.

• 了le: change-of-state particle
• 懂dǒng: to understand

Questions & Answers about wǒ wánquán dǒng le.

What does 了 mean in 我完全懂了?

Here, 了 marks a new situation or change of state.

So 懂 means understand, but 懂了 means something like:

• now I understand
• I've got it
• I understand now

It does not simply mean past tense. It shows that your state has changed from not understanding before to understanding now.

So:

• 我懂。 = I understand / I know it
• 我懂了。 = I understand now / I get it now

With 完全, the sentence becomes stronger:

• 我完全懂了。 = I completely understand now

Is 了 just a past-tense marker here?