Last reviewed . Law current as of October 2026.
After a New Jersey DWI or refusal, you must drive only a vehicle with an ignition interlock for a period set by N.J.S.A. 39:4-50.17: from 3 months for a low-BAC first offense to 2 to 4 years after restoration for repeat offenses. You can install one voluntarily before conviction and, in some cases, earn credit.
Key takeaways
- Interlock periods are set by N.J.S.A. 39:4-50.17 and depend on BAC and prior offenses.
- Installing early (with an MVC notation) can earn one day of forfeiture credit for every two days installed, with exceptions.
- No credit applies to a drug DWI or where serious bodily injury resulted.
How long is the ignition interlock for each BAC level?
| Conviction | Interlock period |
|---|---|
| 1st DWI, BAC 0.08% to under 0.10% | 3 months |
| 1st DWI, BAC 0.10% to under 0.15% | 7 months to 1 year |
| 1st DWI, BAC 0.15% or more | During forfeiture, then 12–15 months |
| 1st refusal | 9–15 months |
| 2nd or later DWI or refusal | During forfeiture, then 2–4 years |
While the requirement lasts you may not drive any vehicle without an interlock. You pay for installation and monitoring.
Can I install an interlock before I'm convicted, and does it help?
Since February 19, 2024, a person charged with DWI may install an interlock before conviction in the one vehicle they own, lease, or principally operate, and request an interlock license notation from the MVC. Credit is one day for every two days installed for a 0.15%+ first offense and for second and third offenses; there is no credit for a drug DWI or where serious bodily injury resulted.
After conviction: for offenses on or after April 3, 2025, P.L.2025, c.41 lets a person required to forfeit driving privileges under 39:4-50 install an interlock instead and earn a one-day credit against the forfeiture for every two days installed. The same exclusions apply: no credit for a drug DWI or if the DWI caused serious bodily injury.
Do the 2024 DWI interlock changes expire in 2029?
Under current law, the interlock provisions of P.L.2019, c.248 and P.L.2023, c.191 expire on January 1, 2029, as does P.L.2025, c.41 (Directive #04-24). Check the date at the top of this page before relying on these rules.
Related guides
- First-offense DWI
First DWI in New Jersey? Fines, IDRC, possible jail, license forfeiture, and interlock by BAC level under N.J.S.A. 39:4-50, plus pre-conviction interlock and the 2029 sunset.
- Breath test refusal
Charged with refusing the Alcotest in New Jersey? Refusal penalties under N.J.S.A. 39:4-50.4a, what the State must prove, how refusal differs from DWI, and common defenses.
- Alcotest 9510
The NJ Supreme Court lifted its stay of Alcotest 9510 DWI cases on December 19, 2025 without ruling on reliability. What that means for pending DWI cases and how results can be challenged.
- Second and third DWI
Second or third DWI in New Jersey? Mandatory jail, fines, community service, license forfeiture, interlock periods, the 10-year step-down, and how out-of-state priors count.
- Driving while suspended (39:3-40 / 2C:40-26)
Penalties for driving on a suspended license in New Jersey under N.J.S.A. 39:3-40, the extra penalties during a DWI suspension, and the fourth-degree crime in 2C:40-26.
Frequently asked questions
Does a first drug DWI require an interlock?
No. The first-offense interlock rules in N.J.S.A. 39:4-50.17(a) cover alcohol and BAC cases and refusals. A first drug DWI carries a 7-month to 1-year forfeiture instead. Any second or later DWI requires an interlock.
Can I drive someone else's car while I have an interlock requirement?
Not unless that vehicle has an interlock. The requirement applies to any vehicle you drive.
Can I get credit for installing an interlock early?
For a 0.15%+ first offense and for second and third offenses, you can earn one day of credit for every two days installed, with exceptions for drug DWIs and serious bodily injury cases. For offenses on or after April 3, 2025, P.L.2025, c.41 also allows the same 1-for-2 credit when you install an interlock instead of forfeiting after conviction, with the same exceptions.
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Sources
This page provides general information about New Jersey law. It is not legal advice, and reading it or contacting us does not create an attorney-client relationship. Every case is different and no outcome is guaranteed.