Delta's credit cards are offering up to 100,000 miles for a limited time - here are the 5 best ways to use them to book flights

• You can earn Delta SkyMiles by flying Delta, as well as by using the airline's co-branded credit cards such as the Delta SkyMiles® Gold American Express Card and the Delta SkyMiles® Platinum American Express Card.
• Until April 1, Delta credit cards are offering elevated welcome bonuses - you can earn as many as 100,000 SkyMiles.
• There are countless ways to redeem your SkyMiles, but some options are better than others in terms of the value you'll receive.
• Top options include booking business class to Europe on Air France and using Delta miles to book flights within the US.
• See Business Insider's list of the best airline credit cards.

Delta is currently the world's second-largest airline, and if you live in a hub city like Atlanta, New York, or Seattle, it may be your carrier of choice. Because Delta's route network is so ubiquitous inside the US and because Delta SkyMiles are (relatively) easy to get, there are many different options for redeeming your miles with Delta and its partners in the SkyTeam alliance - though not all of them offer the best value.

In this article, we'll take a look at the "sweet spots" for using Delta SkyMiles to book award flights.

Keep in mind that we're focusing on the rewards and perks that make these credit cards great options, not things like interest rates and late fees, which will far outweigh the value of any points or miles. It's important to practice financial discipline when using credit cards by paying your balances in full each month, making payments on time, and only spending what you can afford to pay back.

How to earn Delta SkyMiles

The most obvious way to earn Delta SkyMiles is to fly on Delta. Within the past several years, Delta has changed its earning structure, so the number of redeemable miles that you earn on most Delta flights is calculated by your elite status and the total cost of the fare.

Another way to earn a lot of Delta SkyMiles in a short amount of time is with the welcome offers on the different varieties of the American Express co-branded Delta credit cards.

Until April 1, the offers on these cards are elevated, in some cases to their all-time highs.

Delta offers the following consumer credit cards:

• No annual fee: Delta SkyMiles® Blue American Express Card - Earn 15,000 miles after you spend $1,000 in the first three months.
• $99 annual fee (waived the first year): Delta SkyMiles® Gold American Express Card - Earn 60,000 miles after you spend $2,000 in the first three months, and earn an additional 10,000 miles after your first cardmember anniversary.
• $250 annual fee, companion certificate each year: Delta SkyMiles® Platinum American Express Card - Earn 80,000 miles after you spend $3,000 in the first three months, and earn an additional 20,000 miles after your first cardmember anniversary.
• $550 annual fee, includes Sky Club and Centurion lounge access: Delta SkyMiles® Reserve American Express Card - Earn 80,000 miles and 20,000 Medallion Qualification Miles (MQMs) after you spend $5,000 in the first three months, and earn an additional 20,000 miles after your first cardmember anniversary.

If you qualify for a small business credit card - either by running your own business or by doing some freelance work - you could be eligible for one of Delta's three business credit cards:

• $99 annual fee (waived the first year): Delta SkyMiles® Gold Business American Express Card - Earn 60,000 miles after you spend $2,000 in the first three months, and earn an additional 10,000 miles after your first cardmember anniversary.
• $250 annual fee: Delta SkyMiles® Platinum Business American Express Card - Earn 80,000 miles after you spend $3,000 in the first three months, and earn an additional 20,000 miles after your first cardmember anniversary.
• $550 annual fee: Delta SkyMiles® Reserve Business American Express Card - Earn 80,000 miles and 20,000 Medallion Qualification Miles (MQMs) after you spend $5,000 in the first three months, and earn an additional 20,000 miles after your first cardmember anniversary.

Read more: The best small business credit cards

Having an airline credit card can get you additional perks when you fly. In addition to all of the bonus SkyMiles, several of these Delta credit cards come with benefits including free checked bags and priority boarding order.

Now let's take a look at five. of the best ways to use Delta SkyMiles to book flights.

Delta

It may not be the most glamorous redemption, but one of the best uses of your SkyMiles can be to just fly you domestically with Delta where you want to go, when you want to get there. This holds especially true if you live at or near a Delta hub or focus city.

Remember too that if you're short on Delta SkyMiles, you can transfer American Express Membership Rewards points 1:1 to SkyMiles to top off your SkyMiles account.

Delta award "sales"

Several years ago, Delta was the first airline to remove its award chart. Now, the price of a flight in SkyMiles varies based on the route, the date, the time, number of stops, and anything else that Delta decides. Oftentimes the price in SkyMiles correlates to the cash price of a flight, though not always. At least Delta offers weekly award "sales" from either North America, Europe, or Asia.

The removal of the award chart is why I put the word "sales" in quotation marks. If there is no standard and listed price, how can something be "on sale"? That doesn't stop Delta from marketing these as sales, and it is certainly true that you can find some pretty good deals on redemptions from these award sales.

Business class from the US to Europe on Air France

Because Delta no longer has an award chart, it's not as easy to get outsized value from your SkyMiles when flying on Delta-operated flights. But because Delta is a member of the SkyTeam alliance, you can use your Delta miles to fly on Delta's alliance and other partners such as Air France, China Eastern, Air Tahiti Nui, and Korean Air.

One example of a potential sweet spot is from the US to Europe on Air France.

That should cost as few as 75,000 SkyMiles plus taxes and fees. From the United States, those fees typically come out to $5.60 per ticket.

Economy from the US to Australia

15 hours in economy may not sound like the most enjoyable time in the world, but you can get from the US to Australia pretty consistently for only 40,000 Delta SkyMiles, plus taxes and fees.

Depending on the day and route, you may be able to find round-trip tickets to Australia for only 70,000 SkyMiles.

And upgrading to Comfort+ would be a spectacular use of only 10,000 miles extra per person (80,000 SkyMiles total) for more comfort on nearly 30 hours of flying!

Business class from the US to Asia on Korean Air

SkyTeam partner Korean Air flies from Seoul-Incheon airport to Chicago, Washington Dulles, Atlanta, Dallas, Las Vegas, Los Angeles and New York JFK among other destinations. You can get a one way business class ticket from the US to Seoul as low as 85,000 SkyMiles. You'll need to choose dates with partner award space open, but availability is not bad.

Hopefully these ideas have sparked your interest in earning and redeeming Delta SkyMiles.

Unlike some other airlines, Delta doesn't charge any extra fees for booking award flights close to the departure date, so if you have a last-minute trip coming up, you may be able to find a good deal using SkyMiles.

Click here to learn more about Delta's credit cards »

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Please note: While the offers mentioned above are accurate at the time of publication, they're subject to change at any time and may have changed, or may no longer be available.