Tzedaka From Bitcoin

I have a question about giving charity (tzedakah) using cryptocurrency like Bitcoin, which can change in value quickly. According to Jewish law, when I donate using cryptocurrency, should the amount of charity be based on its value when I decide to donate or when the donation actually goes through?

Halacha has no problem with the use of a virtual currency between traders.

However, since Bitcoin is not officially recognized by any government, is not government-issued, and public reliance on it is limited, it cannot be considered as normative currency in Jewish law. It is more like a “secret society” of sorts. Therefore, its halachic status is more like a “commodity” or “debt bond” than transferable money.

As such, you should consider the amount of charity given through a Bitcoin donation by the amount/value the recipient actually receives.

For examples of valid transactions via "invisible" currency see: Kiddushin 2a; Kiddushin 63a, Even Ha'ezer 28:10,13,15.