Amazon will now let Prime members pick which day to get their items delivered, and it's a stealthy way for the company to cut down on its fastest-rising cost

AP/Gene J. Puskar

Amazon will now let Prime members pick their own delivery day.

• Amazon has announced "Amazon Day," an initiative that lets customers pick the day of the week they want their Amazon orders to be delivered.
• All orders designated for the Amazon Day made that week will be delivered on that day grouped in one shipment.
• It can be convenient for customers to know exactly what day an order is going to be delivered.
• It also helps Amazon lower it's ballooning shipment costs by processing and fulfilling fewer orders with fewer of them needing to get to the customer in two days or less.

Now, Amazon day can be whatever day you want it to be.

Amazon Prime members can now designate a day of the week to have all their shipments delivered. The initiative is called "Amazon Day." Customers can also switch around their Amazon Day from week to week if their ideal delivery date changes.

Here's the way it works:

• A Prime member designates a day of the week as their "Amazon Day."
• When a customer makes an order, they can choose their Amazon as part of the shipping page. Or, they can choose Prime shipping like normal.
• When the day arrives, all items that were designated for that shipment will arrive in as few boxes as possible.

This can be convenient for customers for a few reasons. If a customer is worried about theft, they can pick a day where they are home during the day. If they don't need it right away and are concerned about the environment, they can cut down on the environmental impact

It also can be more predictable than a bunch of separate orders.

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"Amazon Day adds another level of convenience to the many shipping benefits Prime members already enjoy. Prime members can now choose to get their orders delivered together in fewer boxes whenever possible on the day that works best for them," Maria Renz, VP of delivery experience at Amazon, said in a statement.

But the real benefits may be for Amazon. This offers customers an easy way to group their items up into as few shipments as possible, making it cheaper and easier to fulfill.

In the test that Amazon ran before launching the full service, Amazon says it already saw a huge amount of savings.

"We've been testing this program with a group of Prime members and Amazon Day has already reduced packaging by tens of thousands of boxes - a number that will only continue to grow now that the program is available to Prime members nationwide," Renz said.

That also may help lessen Amazon's ballooning cost of fulfilling Prime shipping, which has jumped in recent years.

Amazon's fulfillment costs reached $25.2 billion in 2017, up 43% from 2016. Estimates from Benchmark analyst Daniel Kurnos peg 2018's number at nearly $10 billion more, jumping to $43.3 billion in 2019.

As Prime shipping becomes the norm and more customers rely on it for speed and convenience, we'll likely see Amazon come up with more scenarios that convince customers they don't always need their items in two days flat.