What is the difference between Have had and had had?

Answer 1

The verb had is the past tense form of the verb to have.

Examples:

I had £20, but now I don't. (past tense)

At this very moment, I have £20. (present tense)

Used together (have had) is the present perfect tense, used for actions that occurred in the past at different times, suggesting the process is not complete and more such actions are possible.

Example: I have had very little money recently.

Answer 2

This is a brief, non-technical answer; I'm just addressing the difference in meaning. Start with the verb to eat. I have eaten means that as of the time of the statement, my action of eating is completed. The last bite may still be moving down my esophagus as I say it. "I have eaten all of my vegetables." The action is completed, or 'perfected', as of the time of the statement. I had eaten means that my action was completed at some time in the past. "At the time that Mary arrived in Paris, I had eaten all of my vegetables." The action of eating my vegetables was completed at some time in the past; I could be talking about a year ago, or any time in the past.

If you have a sensitive enough ear, then this will sound very awkward: "At the time that John arrived, I have eaten all my spinach." It's a terrible clash of tenses. It's a little like saying "Yesterday, I eat my spinach."

Using these tenses with the verb to have seems odd, because of the repeated word in I had had. But the same way of looking at the meanings applies. The act of 'having' whatever it is was completed at some time in the past. "By the time I was 20 I had had all of my wisdom teeth removed."
Have had is in the present perfect tense. This tense indicates an action or condition that began in the past and is completed as of the present time or continues into the present. This tense is formed in the example from the simple present form of the helping verb to have, which is has or have; plus the third principal part, the past participle, of the main verb to have, which is had.

Had had is in the past perfect tense. This tense indicates an action or condition that was completed by a certain time in the past. This tense is formed in the example from the simple past form of the helping verb to have, which is had; plus the third principal part, the past participle, of the main verb to have, which is had.

Answer 3

'Have' is present tense, whilst 'had' is past tense. i.e. Today I have $10. Yesterday I had $10.

Answer 4

Have means what you've got now and have had means what you used to have or have had before.

Answer 5

"Had" is past tense and refers to possession or ownership in the past.

"Have" is present tense and refers to possession or ownership at the present moment.