How to change or extend a rental car booking

Changing a booking before pickup

Enterprise Rent-A-Car directs customers who are making, modifying or cancelling a reservation to its reservations help pages and offers a View/Modify/Cancel reservation tool on its website. [4]

SIXT sets out a separate, tighter timeline for prepaid bookings in its United States rental information. [7] The table below summarises those conditions as they stood on 18 October 2026.

Because a prepaid rate is charged before the rental begins, at the estimated total for the agreed period, a change is being made against a bill that has already been settled in USD at the exchange rate in force at the time of debit. [7] SIXT adds that any changes made to a prepaid reservation may impact the rental rate. [7]

Extending a rental while you have the car

SIXT asks renters who need more time to visit sixt.com/service or call +1 888 SIXT CAR (749 8227). [7] A rental can be extended until the 28th day of that rental, provided the renter's driver's licence is valid throughout the new period, the incremental authorisation on the payment method on file is processed successfully, and the vehicle selected has enough remaining days and mileage to fulfil the new period. [7] Any extension past the 28th day of the current rental agreement must be handled as a new rental agreement. [7]

Longer bookings follow the same 28-day cadence. A reservation can be made for up to 365 days, and anything over 28 days is processed in 28-day increments until the full length is covered. [7] The first rental agreement is given to the renter at pick-up; later agreements are created remotely and emailed, and the renter must review, sign electronically and supply the vehicle's current mileage for each one. [7] For an ongoing series, SIXT emails a link to accept the next agreement three days before renewal, repeats the reminder one and two days before the new period begins, and treats a missing acceptance as auto-acceptance. [7]

Staying in the car without telling SIXT is not a valid extension. The flexible-return terms state that nothing in them gives the renter permission to keep the vehicle beyond the date and time stated in the rental agreement, and that holding it without contact triggers the standard overdue process. [7]

What a change does to the price

A rental day at SIXT is each consecutive 24-hour period beginning after the start time of the rental, ignoring time zones and daylight-saving shifts. [7]

Under the Flexi Late Return rules, which SIXT applies to both the Pay later/Flexible and Pay now/Best Price rate options, returning the vehicle later than agreed may mean additional full or partial days are charged because of the rental extension, priced on the shorter hire duration. [7] If the renter does not report the extension, SIXT may add a USD 20.00 Flexi Return service fee. [7]

Shortening a rental works differently. On a Pay later/Flexible rate, an early return is charged under the contract terms, and SIXT reserves the right to recalculate on the days actually used, with a partial refund for unused days; its table lists an early-return refund of 50% of the price difference, with a maximum amount payable by the customer for early returns of USD 200.00. [7] On a Pay now/Best Price booking there is no refund for an early return, and once the vehicle is rented no refunds or credits are issued for unused rental days. [7]

Exceptions and limits

• Branch-only extensions. SIXT's non-airport locations in Texas and Illinois do not offer rental extensions over the phone; the customer must come into the branch in person to extend. [7]
• Cancellation fees. A prepaid SIXT booking can be cancelled before the start of the rental. A cancellation up to 24 hours before the scheduled pickup time results in a $100 cancellation fee excluding tax, with the remaining prepaid amount of more than $100 excluding tax refunded; a cancellation within 24 hours of the scheduled pickup time results in a $200 cancellation fee excluding tax, with the remaining prepaid amount of more than $200 excluding tax refunded. [7] Changes or cancellations made within 24 hours of booking are free of charge if the scheduled pickup is more than 48 hours away, and no refund is issued after the scheduled pickup time. [7]
• No-shows and late collection. A prepaid SIXT rate refunds nothing for failure to collect the vehicle, for collecting it late or for returning it early. [7]
• Payment method changes. To change the payment method on file during an open SIXT rental, or at vehicle return, the renter has to visit the nearest SIXT location, and a refund to the original payment method may take up to 15 business days. [7]
• Failed renewal payments. If a payment in a long-term SIXT series fails, the renter is emailed a link to supply another payment method; if SIXT cannot reach the renter after three days, the vehicle must be returned within 24 hours of notice or the overdue process applies. [7]

Frequently asked questions

Can I simply keep a rental car for an extra day?

No. SIXT requires the renter to report a change of plans before the agreed return time, and retaining the vehicle without contact brings the standard overdue process into play. [7]

How late can I change a prepaid SIXT booking?

Up to one hour before the start of the rental, depending on availability, and the rate itself may change as a result. [7]

Does an extension keep the same daily price?

Not necessarily. A late return may be billed as additional full or partial days priced on the shorter hire duration, and an unreported extension can attract a USD 20.00 Flexi Return service fee. [7]

Can I switch a prepaid booking to pay at the counter?

No. SIXT does not allow a change from a prepaid rate to a non-prepaid rate. [7]

How long can a single SIXT reservation run?

Reservations can be made for up to 365 days, with anything beyond 28 days processed in 28-day increments, each with its own rental agreement. [7]

Related pages

If a change turns into a cancellation, see cancellation and no-show policy. For shorter rentals see early return refunds, and for longer ones late return and grace periods. To weigh rate types before booking, read prepaid vs pay at counter, and for definitions see the glossary.

Sources

Sources accessed on 18 October 2026. Other rental companies are not covered here.

1. Enterprise Rent-A-Car car rental FAQs, checked 18 October 2026
2. SIXT rental information for the USA, checked 18 October 2026