What BMI Measures and Why It Matters
Body mass index is a number derived from your weight and height, calculated by dividing weight in kilograms by height in metres squared. It has been used for decades as a rough indicator of whether a person's weight falls within a healthy range for their stature. The standard categories are underweight below 18.5, normal weight between 18.5 and 24.9, overweight from 25 to 29.9, and obese at 30 or above. While BMI does not distinguish between muscle and fat, it remains a useful baseline for most people tracking their health over time.
The main limitation of BMI is that it does not account for body composition, age, or sex. A muscular person may register as overweight despite having low body fat, and older adults may have a normal BMI while carrying excess fat. Still, for everyday use, it provides a simple and consistent measure that can be tracked without special equipment.
Why On-Device Calculation Matters
Many health apps require you to create an account, link to a cloud service, or sync data across devices. This convenience comes with a trade-off: your measurements are stored on servers you do not control. For people who prefer to keep their health data private, an on-device calculator offers a straightforward alternative. All your inputs and results stay on the phone, and no account is needed to use the app.
BMI Mate is a no-account BMI calculator that runs entirely on your device. It accepts both metric and imperial units, letting you switch between kilograms and pounds, or between centimetres and inches, without changing any settings. The app presents your BMI on a colour dial that turns green, yellow, or red depending on which category your result falls into. This visual feedback makes it easy to see at a glance whether your weight is in a healthy range.
How to Use BMI Mate
Open the app and enter your height and weight. If you prefer imperial units, select pounds and inches; if you use metric, enter kilograms and centimetres. The app calculates your BMI immediately and displays it on the colour dial. You can also set a weight goal and track your progress over time. The goal tracking feature is available in the subscription tier, along with additional calculators for basal metabolic rate and waist-to-height ratio.
The basal metabolic rate calculator estimates how many calories your body burns at rest, based on your height, weight, age, and sex. The waist-to-height ratio provides another measure of health, suggesting that a waist circumference less than half your height is a good indicator of low risk. Both calculators are useful complements to BMI for people who want a fuller picture of their body metrics.
Once you have entered your data, you can revisit the app later to check your BMI again, update your weight, or review your goal progress. The app does not require you to sign in or connect to any service, so your data remains on the device. If you prefer a free version, BMI Mate includes ads on the free tier, while the subscription removes ads and unlocks the goal tracking and additional calculators.
When to Track Your BMI
Tracking your BMI is most useful when you are making changes to your diet, exercise, or lifestyle. Measuring your weight regularly and recording it in the app gives you a clear record of whether your efforts are having the desired effect. If you are trying to lose weight, you can set a target and watch the colour dial shift as you approach it. If you are maintaining your weight, you can use the app to confirm that you are staying within your desired range.
It is worth noting that BMI is only one measure of health. If you are very muscular, very tall, or very short, your BMI may not reflect your body composition accurately. In those cases, the waist-to-height ratio or other measures may be more informative. BMI Mate makes it easy to use multiple measures side by side, so you can choose the one that works best for your situation.
Getting Started
To begin tracking your BMI, download BMI Mate from the App Store. Enter your height and weight, select your preferred units, and see your result on the colour dial. If you want to set a goal or use the additional calculators, you can subscribe to unlock those features. If you prefer to keep things simple, the free version with ads is sufficient for most people. Either way, your data stays on your device, and you do not need to create an account or sign in to use the app.