Can I donate less than $1 to Ubuntu?

Yes You can do it.

1. Go to Help shape the future of Ubuntu...

2. Set all input value to 0

3. But in last input do this steps:

At first, Right click on the last input and select inspect element And then set the value to 0.5 (exp.)

then click on Pay with PayPal

And you will see this:

Regular donation?

You cannot give less than 1$ to ubuntu via the standard contribution page.

There is probably a practical reason for this: receiving payments also costs money. If payments are small (here < 1$) it will cost more money to accept the payment/contribution than the money that Ubuntu will make with the contribution. This could be exploited and hence the form on the contribution page does not allow it.

Alternatives?

If there is a particular reason why you want to donate this amount, you could contact canonical. If not, you could try to do something good for the community (ask questions here, for instance) instead of paying something for ubuntu.

As you know Ubuntu is opensource. Here is what you could do if you really want to give your amount.

1. Choose a core dev (maybe someone who maintains a package you like). Check https://launchpad.net/~ubuntu-core-dev for instance
2. Check whether s/he has a https://gratipay.com/ account.
3. If so, you can donate very small amounts (-1$) to that person or to a number of people. This might be on a weekly basis, but I guess you could drop out quite soon.

No, not through a donation: The website where the donation page is shown when you download Ubuntu accepts decimals in the input but it does not accept it after you confirm and will change it to a whole dollar minimum. Simple reason: it probably will cost more to accept the amount than the amount itself.

But there is a way. Sort of. The closest you get to 0.50 is through the Ubuntu shop: Kubuntu Ballpoint Pen White/Blue at the moment costs 0.63 USD (normal price is 1.11 USD). So if you consider the 0.50 USD a donation, the pen would cost you 0.13 USD. Shipping excluded...