The free-shipping competition has heated up among online retail giants—meaning shoppers can save more money at certain sites. Amazon.com recently lowered the minimum order required for free shipping for the second time this year, from $35 to $25 for delivery within five to eight days for non-Prime members. In January, Walmart.com introduced free two-day shipping on orders of at least $35. In contrast, Target recently raised its minimum order for free shipping from $25 to $35 for shipping in three to five days…but Target credit card and debit card holders get free shipping automatically.

Caution: Not all items qualify for free shipping even if you meet the minimums. When you comparison shop online, factor in the total cost of an item—purchase price plus shipping—as well as how soon you’ll need it.

Studies show that when shoppers don’t have to pay for shipping, they increase their order sizes by an average of 30%. Walmart has also been experimenting with discounts for customers willing to have certain purchases shipped for free to a Walmart store for pickup by the customer. The discount can be as much as $50 off purchases of large items such as TVs when you choose local store pickup on the website. Amazon customers get free two-day shipping on many items with no minimum required if they sign up for an Amazon Prime membership, which costs $99 annually and includes a host of other services such as unlimited streaming of movies and music.

Free shipping policies at other major online retailers…

Staples requires a low $14.99 minimum for free standard shipping as long as you provide your rewards loyalty member card at purchase, although certain oversized items are excluded. Like Walmart, Staples lets you avoid shipping charges by purchasing any item online and picking it up at a Staples store.

Best Buy provides rewards club members free two-day shipping on thousands of items with a minimum purchase of $35. Qualifying items display a “Free 2-Day Shipping” message on the website.