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 in the middle of the range 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 71.6, which rounds to 72. 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.