Cheapest way to ship your package? Here's how to save.

Post office beats UPS, FedEx on price in a head-to-head comparison, more than $50 on an overnight five-pound package. But don't go to the post office. There's a better way.

Santa and his reindeer have fierce competitors in FedEx, UPS, and the US Postal Service. The three shipping providers expect to deliver more than 1 billion packages this holiday season and need only one night to deliver a gift by the next morning.

But unlike St. Nick, you have to pay the delivery charges yourself. Which of the three shippers offers the cheapest rates?

Cheapism.com recently sought out cheap shipping methods from all three providers, comparing prices for 5- and 10-pound packages sent from New York City to residential addresses in Chicago and San Francisco. In every case, from ground delivery to next-day service, the Postal Service undercut the private companies.

Take that overnight package with delivery the next morning. UPS and FedEx charge the same hefty price: $91.76 for a five-pound package from New York to San Francisco, for example, with delivery by 10:30 a.m. At the post office, guaranteed delivery by noon costs $52.20 – or, if you print your own shipping label and schedule a free pickup, only $39.14. That’s a difference of only an hour and a half but a potential savings of more than $50.

FedEx and UPS do promise certain benefits in exchange for their higher prices. Both provide point-by-point tracking and money-back guarantees for all the services Cheapism researched. The only Postal Service option that includes those perks is the most expensive, Express Mail, which offers overnight delivery to most domestic locales.

In general, consumers will find more shipping methods with guaranteed delivery times at UPS and FedEx but also many caveats in the fine print. Don’t expect a refund if the weather outside is frightful, for example, or if it’s too close to Christmas. FedEx and UPS are suspending their guarantees for ground delivery beginning on Dec. 11. They will still cover faster, pricier deliveries that arrive even one minute late through Dec. 18, when their guarantees will kick in only for delays of more than 90 minutes.

The very cheapest (and, naturally, the pokiest) shipping method overall is Media Mail, a post office service that’s limited to “educational materials,” but encompasses gifts such as books and DVDs. In Cheapism’s comparison, it cost only $4.15 to send a five-pound package and $6.19 to send a 10-pound parcel via Media Mail. The estimated delivery time was eight days.

For other gifts, the post office’s Parcel Post costs less than FedEx Home Delivery or UPS Ground but also takes longer: an estimated six days to Chicago and eight days to San Francisco, compared with two days to Chicago and five days to San Francisco with one of the private couriers.

Depending on the weight of the package, it may actually be cheapest to go with Priority Mail flat rate from the Postal Service, which takes just two or three days for most destinations. Flat-rate boxes ship for a fixed price, no matter where they’re headed or how much they weigh (up to a maximum of 70 pounds). Shipping a 10-pound package in a flat-rate box to San Francisco costs $10.85, compared with $17.29 for parcel post (which would also take five days longer) and $55.10 for three-day service from FedEx or UPS. Flat-rate boxes are available for Express Mail as well and come in a variety of sizes.

Another tip for Postal Service customers: Priority Mail and Express Mail cost less if you visit usps.com instead of the post office. The price of sending a 10-pound package to San Francisco from New York via Express Mail is $53.69 online vs. $76.95 at the post office. Customers can order free supplies, print labels, and schedule free pickups. UPS and FedEx offer similar services but no discount for online shipping.

In its comparison of the three shipping providers, Cheapism also weighed factors such as customer satisfaction and convenience. The Postal Service maintains more than 35,000 retail offices, including many in remote areas, dwarfing the number of FedEx and UPS outposts. It has cut business hours at many of those rural Post Offices, however, while the private companies each count more than 40,000 drop boxes where customers can leave packages 24/7.

The Postal Service is the only provider that delivers six days a week at no additional cost. UPS and FedEx typically charge an extra $15 for Saturday delivery, with the exception of FedEx Home Delivery, which operates Tuesday through Saturday.

Cheapism’s full comparison also touches on e-commerce and reviews various ways to earn free online shipping. Even the Postal Service can’t beat that price.

– Kara Reinhardt is associate editor of Cheapism.com, a review site dedicated to finding high-quality, low-cost products.