A calorie-tracking app knows what you eat, when, how much, and, over time, a fairly complete picture of your health and body. That is a lot of sensitive, ongoing data for an app to collect for free. It is worth asking what actually funds the free tier before handing months of it over.
The two common models
The most common answer is ads. MyFitnessPal's free tier carries them; so does FatSecret's. Ads on a food-logging screen you open five times a day are a genuinely effective, well-understood business, which is exactly why so many apps in this category use it. The other common answer is a deliberately limited free product engineered to convert: enough functionality to be useful, not enough to be complete, so the paid upgrade feels necessary rather than optional.
Neither model is secretly malicious. Both are reasonable ways to fund a free app. But both mean the incentive structure around the free version of the product is not purely "help you track your food as well as possible."
What to actually check
Before trusting a free calorie tracker with months of your eating data, it is worth checking a few concrete things: does the privacy policy mention selling or sharing data with advertisers, is the free tier ad-supported, and are the features that get gated behind a paywall the ones that actually matter for accuracy (portion precision, full macro breakdowns) rather than cosmetic ones. Those answers tell you more about the real cost of "free" than anything in the marketing copy.
Where Arcal stands on this
Arcal is one paid plan, no free tier, no ads, and the food diary is not sold. That is a different tradeoff, not a virtue-free one: paying up front instead of paying with attention or data. See pricing or why we do not have a free tier.