License suspension
A single under-21 DUI typically suspends your driver license for at least six months on a first offense, and longer for repeat offenses. The suspension applies even if your blood alcohol was well below the adult limit. In most states the suspension begins immediately, before any court date.
Insurance impact
A DUI on your record raises your insurance premiums for years — often three to five times your previous rate. Some insurers will not renew the policy at all and you will be required to obtain SR-22 high-risk coverage, which is expensive and often hard to find.
Long-term record
A DUI on your record is visible to college admissions, employers running background checks, and — for many years — to insurance underwriters. Diversion programs exist in some states that can reduce or seal the record after completion, but they involve months of supervision and additional fees.
Plan a ride home
Rideshare is cheaper than a DUI by about three orders of magnitude. Plan how you are getting home before you go out, every single time. Designated drivers are the cheapest plan of all.