How we calculate your Brain Fitness Index
You play a few two-minute games, and at the top of your dashboard a single number appears: your Brain Fitness Index. It's convenient : but a number you can't see the working behind is just a guess with good lighting. So here's the whole recipe, start to finish.
Start with six numbers, not one
Before there's a single index, there are six honest numbers underneath it: one for each cognitive category you train: Memory, Attention, Speed, Flexibility, Problem Solving, and Language. Each carries its own rating that rises and falls as you play games in that skill. Those ratings start at 1200 on a 500–2500 scale and move based on how you do relative to the difficulty you're facing: the same mechanism that drives the adaptive difficulty of your sessions.
Put every skill on the same scale
A raw skill rating doesn't mean much on its own, and the six skills aren't naturally on the same scale. So each one is normalised onto a common 0–100 range first. That's what makes them comparable: a strong Memory and a still-developing Speed can sit side by side and be combined sensibly, instead of one quietly drowning out the other.
Combine them: with weights, in the open
Your BFI is a weighted averageof those six normalised scores. We don't weight them equally: Memory and Attention each count a little more, reflecting how central they are to everyday cognition. The weights are fixed and public, so you can always predict how a gain in one skill will move your overall number:
Memory
20%
Attention
20%
Speed
15%
Flexibility
15%
Problem Solving
15%
Language
15%
100%
BFI = 0.20 × Memory + 0.20 × Attention + 0.15 × Speed + 0.15 × Flexibility + 0.15 × Problem Solving + 0.15 × LanguageEach term is that skill's rating normalised to 0–100. Multiply by its weight, add the six up, and you have a single number from 0 to 100.A worked example
Say your six normalised scores are Memory 78, Attention 70, Speed 65, Flexibility 72, Problem Solving 60, and Language 80. Apply the weights : 0.20 × 78 + 0.20 × 70 + 0.15 × 65 + 0.15 × 72 + 0.15 × 60 + 0.15 × 80: and your BFI works out to 71.15, which rounds to 71. Notice the leverage: lifting a 20%-weighted skill like Memory moves your BFI more than the same gain in a 15%-weighted one. Nothing hidden, nothing magic: just an average you can do on the back of an envelope.
What the number is: and isn't
The BFI exists to answer one everyday question at a glance: “am I keeping up my training, and is it trending the right way?” It's a summary of how you perform on CogDojo's games, measured consistently over time. That's the whole of what it claims to be: and it's most useful read as a trend over weeks, not a verdict on any single day.
One honest note we'll always make: the BFI measures how you do on our games. It is not a medical assessment, and it doesn't claim to measure your real-world cognitive ability, predict health outcomes, or prevent cognitive decline. It's a training metric: useful for staying engaged and watching your own progress, and nothing more than that.