Payton v. Superior Court, 202 Cal. App. 4th 1187

Payton pled guilty to Health and Safety Code possession of a controlled substance in January 2008; sentenced to three years’ formal probation.
In May 2011 Payton admitted probation violation and received a 90‑day jail term with 10 days actual credit and four days conduct credit.
Payton sought day‑for‑day conduct credits under the January 25, 2010 amendment to Penal Code §4019; trial court denied relying on pre‑amendment violation date.
The district attorney argued for prospective application of §4019; the Attorney General conceded error and Payton was entitled to additional credits.
Payton’s custody included pre‑sentence time; he was released July 7, 2011, after petition for writ of habeas corpus.
This court granted relief, treating the petition as a writ of mandate and remanding to recalculate credits under the 2010 §4019 version.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Retroactivity of §4019 amendment	Payton argues the 2010 amendment applies to pre‑sentence time.	State contends prospective application unless retroactivity is expressly stated.	Amendment applied retroactively to Payton.
entitlement to day‑for‑day conduct credits	Payton is entitled to increased conduct credits for pre‑sentence custody under the 2010 amendment.	Credit calculation based on pre‑amendment date of offense is controlling.	Payton entitled to six additional conduct credits; recalculation required.

Palma v. U.S. Industrial Fasteners, Inc., 36 Cal.3d 171 (Cal. Supreme Court 1984) (permits writs of mandate where appropriate)
People v. Alford, 42 Cal.4th 749 (Cal. Supreme Court 2007) (considerations for statutory retroactivity and legislative intent)
In re Estrada, 63 Cal.2d 740 (Cal. Supreme Court 1965) (lingering inquiry into retroactivity when intent is unclear)
People v. Dieck, 46 Cal.4th 934 (Cal. Supreme Court 2009) (definition of conduct credits under §4019)