Last week, I mentioned that pairing dollar coupons with dollar sales at the grocery store are one of my favorite ways to get items for free. Another easy way? Double-coupon days.

Coupon “doubling” occurs when a store matches a coupon’s face value and passes the added bonus savings on to you, the shopper. Here’s how it works. When you go to the checkout and hand the cashier a 50-cent coupon during double-coupon days, the cashier scans it and the cash register automatically doubles the value of that coupon to $1. You receive a dollar savings on one item with one 50-cent coupon.

Grocery stores handle double-coupon promotions differently. Some stores double coupons up to a certain amount every day. Others offer double-coupon promotions on certain days of the week or certain weeks of the month. Still others offer double coupons on some days and triple coupons on others. During a triple-coupon promotion, a 50-cent coupon is worth $1.50.

These sales are definitely worth checking out because stores that double coupons make it very easy for shoppers to get groceries for free or at big discounts. However, in my experience, many stores have specific rules for the ways they double coupons. You’ll want to refer to your store’s coupon policy to determine exactly how your store handles these promotions. Visit the store’s Web site for the information or ask for a copy of the guidelines next time you’re shopping.

For example, one national grocery store chain will double all coupons worth up to 55 cents every day of the week. Another national chain doubles coupons up to $2 each, but they only run this promotion for one week each month. Some stores will double Internet coupons, others won’t. It’s important to find out exactly how your store handles doubles so that you aren’t disappointed at the checkout.

Let’s go back to our example from last week, the “dollar sale” at the grocery store. Our store has many items on sale for $1, including cans of soup, toothbrushes and bags of frozen vegetables. Our store also doubles coupons up to $1 in value. How can we get things for free? Well, any coupon with a value of 50 cents will automatically be doubled to $1. I have a 50-cent coupon for the soup, a 55-cent coupon for the toothbrush and a 75-cent coupon for the vegetables. With those three coupons doubling in value, I’ll be taking home a can of soup, a toothbrush, and a bag of frozen veggies all free.

It’s important to note, too, that coupons typically do not double over the value of the item. This is different from the way some stores handle “overage,” which is when your coupon’s value exceeds the cost of the item you’re buying. At many stores, using a $1 coupon on an item that is on sale for 75 cents will not only give you that item for free, it will also take an extra quarter off your total purchase. This is the overage value that was left over after your $1 coupon paid for your 75-cent item. However, when a store offers double coupons, they’re matching the coupon’s value out of their own pocket. So, using a $2 coupon on a $3.79 bottle of spray cleaner will get you the cleaner for free, as the coupon doubles up to $4, but it will not give you that extra 21 cents in overage. However, you’ll be taking items home for free, and who doesn’t love that?

Now, don’t fret if you no stores double coupons in your area. Coupon doubling tends to be a regional phenomenon. Here in the Chicago area, none of our grocery stores double coupons, ever! The closest stores that do are 45 minutes from where I live. (And yes, I take “coupon field trips” to them on occasion.) But I do the bulk of my weekly shopping in a store that does not double coupons, and I still manage to cut my bill by half or better with coupons each week.

Jill Cataldo writes from suburban Chicago on coupon matters. Her column and some valuable local coupons appear in Thursday editions of The Daily Astorian.

Readers are advised to check with their favorite store’s customer service counter to learn its coupon policy in case it varies from Cataldo’s suggestions. Some regional differences and rules do apply on doubling, overage and other issues.