3-Month Weight-Loss Program

You can accomplish a lot in three months — including serious progress toward your weight loss goals. A healthy three-month weight loss plan includes a nutrient-rich, calorie-controlled diet, plenty of invigorating physical activity and forgiveness for the days when things don't go as planned.

It may be tempting to head straight for "crash diets" that promise quick and dramatic results. Don't do it! These diets promote habits so drastic that they're impossible to maintain over the long term, and the weight comes back on with a vengeance once you return to your usual habits.

Instead, focus on making sustainable lifestyle changes that promote a nutrient-rich diet and healthy levels of physical activity. These will become the cornerstone of your three-month weight loss plan, but they're also likely to become habits that last a lifetime.

That's according to a review of studies on habit formation, published in the December 2012 issue of the British Journal of General Practice, in which the authors note that habits tend to reach their maximum "automaticity" — or become a natural part of your life — after 66 days, or just two months.

Read more: The Best Tips for Every Stage of Your Weight-Loss Journey

You can use the principles of healthy weight loss to create a personalized, three-month weight-loss plan that works for you. Start by consulting the U.S. Department of Health and Human Services (DHHS) table of recommend calorie intakes or the American Council on Exercise daily calorie needs calculator.

Short of recommendations from a registered dietitian or healthcare professional, sources like these — which recommend a calorie intake based on your body size, gender and physical activity level — are one of the best ways to estimate your daily calorie intake.

However, the numbers you get from those sources are for maintaining your weight, not losing weight. According to the Centers for Disease Control and Prevention, a healthy rate of weight loss is 1 to 2 pounds per week. That means you need to burn 500 to 1,000 calories more each day than you're taking in — all without taking your daily calorie intake below 1,200 calories for women, or 1,500 calories for men, as noted by Harvard Health Publishing.

Keep things balanced by aiming to achieve about half of that calorie deficit (250 to 500 calories) by trimming excess calories out of your diet. That means your daily calorie intake should be 250 to 500 calories below the estimates you got for maintaining your weight. So, if you've estimated that a daily diet of 2,000 calories would help you maintain your weight, adjust that to 1,500 to 1,750 calories to lose weight.

Counting calories and measuring portion sizes may not be fun, but it's the most efficient way of determining exactly how much you're taking in, then deciding where you can substitute in smaller portion sizes, healthier versions of your favorite foods, or both.

If you're not sure how to build a balanced diet that focuses on healthy, good-for-you foods, start by following the DHHS key recommendations for healthy eating patterns. Some simple takeaways include:

• Focus on whole grains over refined grains
• Try to eat the entire rainbow (all the sub-groups) of fruits and vegetables
• Aim for a variety of high-quality protein sources, including eggs, legumes, nuts, seeds, soy products, seafood and lean meats
• Choose fat-free or low-fat dairy choices and healthy oils

When in doubt, you can make great improvements in your diet simply by cutting out processed foods. You should also follow DHHS recommendations to limit your sodium intake to less than 2,300 mg per day and consume less than 10 percent of your daily calories from added sugars and saturated fats.

So where's the other half of that calorie deficit going to come from? Exercise. The Centers for Disease Control and Prevention recommendations for physical activity are a great place to start: They recommend getting at least 150 minutes of moderate-intensity aerobic activity per week, or 75 minutes of vigorous-intensity aerobic activity.

This amount of physical activity provides great healthy benefits, but make sure you track your calorie burn with a mobile app or online calculator — in order to meet your weight loss goals you should burn an extra 250 to 500 calories per day.

Reaching that kind of calorie burn doesn't have to mean hitting the gym if you don't want to. You can also burn lots of calories by exercising at home or outdoors. Here are examples of some great calorie-burning activities, both in and out of the gym, based on estimates from Harvard Health Publishing:

• Walking
• Running
• Hiking
• Cycling
• Swimming
• Dancing
• Active sports such as volleyball, flag football, rock climbing and martial arts
• High-impact aerobics
• Circuit training
• Using an elliptical trainer or stationary rower

To burn more calories in less time, consider increasing your exercise intensity as you build strength and confidence.

Read more: Your Straightforward Guide to Getting Started With Cardio

You should also strength-train all your major muscle groups at least twice a week, as recommended by the CDC. This not only makes you stronger, but it also burns more calories and helps boost your metabolism. Compound exercises such as push-ups, chest presses, pull-ups, dumbbell rows, squats and lunges give you the most efficient returns because they work multiple muscle groups at once, and many of them can be done with limited equipment or even none at all.

As you work out, you'll be working toward much more than a slimmer waistline. As the Mayo Clinic notes, regular aerobic exercise packs a number of health benefits, including a stronger immune system, a boost for your mood, lower risk and better management of chronic diseases. The Mayo Clinic also notes the benefits of regular strength training: stronger bones, sharper cognition, improved quality of life and better management of chronic conditions, to name a few.

Read more: Here's Exactly How Beginners Can Start Strength Training

Anybody who sees the results of your three-month weight loss plan will have good reason to be impressed. But it's hard to track your own day-to-day progress in the mirror, simply because daily changes are so much more gradual than what you'll see from day one to the end of your third month.

With that in mind, it's well worth investing a little effort into objective measures of your progress. Taking before and after pictures is a popular method — try to wear the same clothes in all your progress photos and also strike the same poses, so that you can really see the difference your progress is making. You can snap before-and-after pictures on day one and day 90, or try taking monthly progress photos.

Measuring your waist circumference is another easy, inexpensive way of measuring your progress, as explained by the Harvard T.H. Chan School of Public Health. Wrap a flexible measuring tape around the narrowest point of your midsection, using a mirror or a friend's help to make sure the tape is leveland not twisted. Ideally, you should take the measurement over your bare skin. If you prefer to wear a shirt while measuring, be sure to wear the same shirt for future measurements.

You can also track your progress by measuring the circumference of other body parts: the thickest part of your hips, thighs, arms and even your neck are all common places to check your progress. Pay close attention to where you're taking the measurements so you can duplicate that method as closely as possible every time, and write down your measurements so you can see how much progress you've made.