Most people who track their calories are wrong by a few hundred a day, and they have no idea. The gap is rarely dishonesty. It is oil measured by eye, portions guessed on a busy evening, and the weekend that never quite makes it into the app.
Consistency beats precision
Start here, because it changes what you should worry about.
You will never log perfectly. Labels carry a tolerance, restaurant portions vary, and your body absorbs food differently from a calorimeter. Chasing exactness is a waste of effort.
What you can do is log the same way every day. A consistent 5% error is harmless, because it shows up identically in every week's total. The trend on the scale still tells you the truth, and the trend is what you act on.
Inconsistency is what breaks tracking. Logging carefully on weekdays and vaguely at weekends does not give you a small error. It gives you a number that means nothing.
Get a scale, at least for a while
Weighing food is the single biggest jump in accuracy you can make, and you do not have to do it forever.
Weigh things for two weeks and check your guesses. Nearly everyone is badly wrong about at least one item. Oil, cheese, peanut butter, cereal and rice are the usual suspects, and a heavy hand with olive oil can hide 200 calories in a meal that looked virtuous.
Weigh raw where you can, since cooked weights change with water. Once you have calibrated your eye, our guide to estimating portions covers how to keep going without the scale.
Use the app properly
Every food database is full of user-submitted entries, and plenty of them are wrong. Prefer verified entries, and be suspicious of anything that looks conveniently low.
Barcode scanning is fast and accurate for packaged food. It does nothing for the meal you cooked.
Build your own recipes once. If you eat the same chilli every fortnight, entering it properly one time saves you the guesswork for a year.
And log before you eat rather than after. It is more accurate, and it gives you a chance to change your mind about the second portion.
Read the label in the right order
Serving size first, always. Everything else on the panel is expressed per serving, and a packet that reads 200 calories is often two or three servings.
Then calories per serving, then the ingredients list, because a short list of recognisable things is a decent proxy for how the food will behave.
Front-of-pack claims deserve suspicion. Low fat frequently means more sugar. Our piece on why label counts are often wrong explains what the numbers do and do not include.
The things people forget to log
Cooking oil and butter. This is the biggest one by a distance.
Drinks. Juice, beer, wine, and anything from a coffee shop that involves syrup or milk.
Sauces and dressings. A generous spoon of mayonnaise costs more than the chicken it went on.
Tastes and bites while cooking, the chips off someone else's plate, the biscuit with the afternoon tea.
Track a normal week including all of that, and the number is often higher than expected. That gap is usually the entire reason a diet stopped working.
Eating out
You cannot log a restaurant meal accurately, so stop trying. Estimate generously, because kitchens cook with more oil and butter than you do at home.
Where a chain publishes figures, use them. Where nothing is published, pick something similar from the database and add a bit. Consistently overestimating a few meals a week costs you very little, and it keeps you honest.
Set a target you can hold
Work out your maintenance calories, then take 250 to 500 off for fat loss. Aggressive deficits are harder to log accurately, because hunger makes people sloppy.
Review every two weeks using weekly averages rather than single weigh-ins. If the trend is flat when it should be falling, the first suspect is your logging, not your metabolism.
And take a break when tracking starts to feel obsessive. It is a tool for learning what your food actually contains. Once you know, you can put it down for a while.