Nunc pro tunc is Latin for…
How Nunc Pro Tunc Is Used In Criminal Court
In criminal court the term, nunc pro tunc, is used to “back date” a court order.
It’s used when a court or a judge gives an order but is inadvertently omitted from the written record. See People v. Melchor, 226 Ill. 2d 24, 32 (2007); see also Harreld v. Butler, 2014 IL App (2d) 131065, ¶ 13.
To fix this a judge will renew the order nunc pro tunc back to the orginal date.

Because a “nunc pro tunc” amendment may reflect only what the trial court actually did, it must be based on some note, memorandum, or other memorial in the court record.
Example Of How Nunc Pro Tunc Can Be Used
Typically, a nunc pro tunc order or judgment is limited to incorporating into the record something which was actually previously done by the court.
However, it can also be used by a defense lawyer, for example, to back date a custody order so that a defendant is entitled to more credit for days in custody.
Consider People v. Jones
People v. Jones, 2016 IL App (1st) 142582 (August). Episode 217 (Duration 7:23).
A nunc pro tunc order is not a way to predate a court order.
Facts
Defendant was arrested and released on crime A.
Later, he was arrested anew for crime B.
Defendant asked the court to exonerate his bond nunc pro tunc to the arrest date on crime B so that he could get credit on crime A for the time he was in custody for crime B.
The State did not object and presumably intended that the defendant would be considered in custody on charge as well.
Nunc Pro Tunc Order
Nonetheless, the reviewing court said the trial court was in error when it entered the nunc pro tunc for the simple reason that there was no order ever entered that omitted something the court previously did or that needed correction or clarification.
No Pretense
Here is the big one: An order entered nunc pro tunc may not supply omitted judicial action or correct judicial errors under the pretext of correcting clerical orders.
While defendant was on bond in this case he decided to surrender on another unrelated charge. He was never brought before any court on this charge nor did he make any attempt to exonerate his bond until after he was arrested on the other charge.
Defendant Wanted More Credit
Defendant wants credit against this sentence for the time he was in custody on the unrelated charge, claiming a nunc pro tunc order entitles him to the credit even though he did not surrender his bond in this case until he appeared before the trial judge in this case.
(Revoking bond is being used the same way as exonerating his bond.)
Analysis
A defendant who is out on bond on one charge, and who is subsequently rearrested and returned to custody on another charge, is not returned to custody on the first charge until his bond is withdrawn or revoked.
A defendant arrested while on bond remains on bond until the bond is exonerated, at which point the defendant will be considered to be in simultaneous custody on both charges.
Giving effect to the “non pro tunc” order would effectively give the circuit court, the defendant and the State the power to increase the in custody credit beyond the parameters set by the legislature under 730 ILCS 5/5-4.5-100(b).
Holding
The mittimus was ordered to be corrected to reflect the loss of the credit defendant was seeking. The only reason it was before the court is because he was fighting for three additional days, instead he ended up losing 50.
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