WHEN IT COMES TO WEIGHT LOSS, CUT 100 — CALORIES, THAT IS!

SLOW and steady — and perfect for the lazy dieter — we know how you can battle the bulge without doing a whole lot.

So if your “New Year, New You” dieting plan went belly up in mid-January, we’ve got your number.

And it’s 100.

Cut 100 calories a day and, at the end of 12 months, you’ll be 10.4 pounds lighter.

PHOTOS: 100-Calorie Foods

Here’s how it works — 1 pound is equal to 3,500 calories. Cut 100 calories out of your day for 365 days (that’s 36,500 calories a year, genius) and — voila! — you’re going to need dresses that are a whole size smaller.

“A hundred calories is nothing. And it’s something I’m very strict with my patients about,” says Tanya Zuckerbrot, a registered dietician and founder of skinnyandthecity.com.

“I don’t believe in cutting things out completely. That’s bulls—. You can easily reduce your caloric intake and not make a dent in the volume of food or the satisfaction. And you can lose 10 pounds effortlessly.”

The trick is substitution. Swap out your existing high-calorie snack for a 100-calorie option, or make small adjustments during mealtime to help bring your caloric intake down. Either way, you’re sure to end up a big loser. But what do 100 calories look like? Not what you’d expect, that’s for sure.

Here are some quick tips to help trim the fat:

* Choose a Starbucks grande nonfat misto (70 calories) instead of a Starbucks grande latte (190 calories). Switch and save: 120 calories.

* Lunch on a BLT sandwich with three slices of deli turkey, three slices of bacon, lettuce and tomato on whole-wheat bread, a house salad with balsamic vinegar and two tablespoons of Parmesan cheese (400 calories) rather than a tuna-salad wrap, which will cost you 500 calories. Switch and save: 100 calories.

* For a quick snack between blocks, pick two street-meat beef kebabs (330 calories for both) over a pretzel (430 calories). Switch and save: 100 calories.

* In the mood for Japanese? A mayo-free tuna roll (240 calories) is the better choice over its spicy counterpart, which clocks in at 340 calories. Switch and save: 100 calories.

* An average serving of entrée-size pasta is six cups and more than 1,000 calories. Instead, opt for a pasta appetizer — one cup of pasta without sauce is 240 calories. Switch and save: more calories than you can count — plus your waistline.

* Carbs are devilishly good. If you’re out at an Indian restaurant, choose half a piece of naan without butter or one whole-wheat chappati over a cup of rice, which is 240 calories. Love rice? Eat half. A good rule to remember: One ounce of any bread is generally equal to 80 calories. Switch and save: 160 calories.

* For a takeout fix, pick hot and sour soup over the wonton soup — each piece of doughy goodness is 50 calories. Switch and save: between 100 and 150 calories.

* Salads are healthy until you drown every last leaf in lots of oil and vinegar. Ditch the oil — each spoonful of extra virgin is 135 calories — and dress the salad with balsamic vinegar and one tablespoon of grated Parmesan cheese. Switch and save: 110 calories.

rmirchandani@nypost.com