The Mental Fatigue Calculator looks at one specific question inside chronobiology and recovery science: what do your mental fatigue actually add up to? Instead of a vague feeling, it converts the everyday signals you already notice — daily recreational screen time, bedtime consistency, awake hours in bed daily, actual sleep per night — into a single score you can track, compare and act on.
The model is built on circadian research, sleep science and behavioral-energy modeling, the same foundation as our flagship routine calculator. Each input is weighted by how strongly that factor predicts real outcomes in the research; the formula and every weight are published below, so you can see exactly why your score is what it is — and argue with it if you like.
Adjust the sliders to match your situation honestly and the score updates live, along with the strongest factors pushing it up or down. Like everything on Quirkulator, the computation runs entirely in your browser: nothing you enter is ever transmitted or stored.
The formula
w1·screen h- Daily recreational screen time (weight +0.9)
w2·sleep consistency- Bedtime consistency — 0 = chaos, 10 = same hour nightly (weight -0.8)
w3·in bed awake- Awake hours in bed daily (weight +1)
w4·sleep h- Actual sleep per night (weight -0.9)
w5·caffeine late- Caffeine after 2pm (weight +0.5)
σ, μ- Sigmoid squash to 0–100, centered on typical values
How it works, step by step
- Rate each input honestly — the Mental Fatigue score is only as good as your self-assessment.
- Watch the live score and note which factor the result panel names as your strongest driver.
- Read your band below — each range comes with a concrete recommended next step.
- Change one input to simulate a change in behavior and see how much the score moves — that sensitivity is the real insight.
- Re-take the assessment after a few weeks; trends across readings mean far more than any single score.
Worked examples
A low-signal scenario
With every input set well below typical — the quiet version of this situation — the model returns 70, landing in the “Running on debt” band. Your light, movement and sleep signals are working together. Whatever tiredness you feel is probably load, not rhythm — and recovers with normal rest.
A high-signal scenario
Push the main drivers well above typical and the score rises to 50 — the “Minor drift” band. Your circadian system is likely running hours later than your obligations, and bed has become a stimulation zone. Gradual, consistent corrections beat heroic resets — and if exhaustion persists regardless, involve a professional.
How to read your score
Frequently asked questions
What does my Mental Fatigue Calculator result mean?
It is a composite of the levers chronobiology says drive daily energy: light timing, sleep regularity, movement, and how much awake time leaks into bed. The bands translate the number into what your body is likely experiencing.
What is a circadian phase delay?
Your internal clock drifting later — melatonin rising later at night, natural wake time sliding forward. Dim-light awake hours are the main driver; morning outdoor light is the main correction.
What is the highest-leverage fix?
Ten minutes of outdoor morning light. It anchors the circadian clock, cancels most accumulated phase delay, and improves that night’s sleep — the cheapest intervention in all of sleep science.
When should I see a doctor rather than a calculator?
If fatigue persists despite reasonable sleep, or low mood and energy last more than two weeks, that pattern deserves a professional — persistent exhaustion has medical and psychological causes no lifestyle calculator can assess.
Is spending a day in bed actually harmful?
An occasional recovery day is fine and arguably restorative. The research concern is chronic pattern: regular awake hours in dim light delay your circadian phase, suppress energy expenditure toward resting rate, and detrain the sleep-bed association.
Is my health data stored?
No. All computation runs locally in your browser; nothing is transmitted or saved.