Will the new Penal section 4019 apply if i've already been sentenced to 4 years in prison and i'm appealing now while in jail?

Unfortunately, the answer is still a little unclear.

According to a memo circulated this week to all California judges, the new 4019 credits may apply retroactively to all cases that are not yet final by January 25, 2009. That would include cases where the defendant has been sentenced to prison, but the appeals are not exhausted.

For instance, under the prior version of Penal Code 4019, if you had served 60 actual days prior to sentencing, you would be entitled to 80 days of credit, including the 20 days for good conduct.

Note that defendants who have a prior "strike," are convicted of serious or violent felonies, as defined by the Three Strikes law, or convicted of an offense that carries sex offender registration are not eligible for the new half time credit.

Please understand that this is a general discussion of legal principles by a California lawyer and does not create an attorney/client relationship. It's impossible to give detailed, accurate advice based on a few sentences on a website (and you shouldn't provide too much specific information about your legal matter on a public forum like this site, anyway). You should always seek advice from an attorney licensed in your jurisdiction who can give you an informed opinion after reviewing all of the relevant information.

No. 4019 applies only to county jail time. Since you are in the big house there's no change for you. Sorry.

PC 4019 only covers good time & work time credits for local (county) jail time. If you're in state prison, this code section doesn't help you.

I wish you the best of luck with your appeal.