Every page on this site is generated by a small set of transparent models. Here is exactly what each one does — so you can decide whether to believe the output.
Future value of a regular contribution, compounded monthly: FV = P × ((1 + r)ⁿ − 1) / r, where P is the monthly deposit, r the monthly rate and n the number of months. Savings default to 4.5% APR, investing to 8.0%. Figures are nominal: no inflation, no tax on interest.
A month-by-month amortisation loop. Interest is added, then the payment (minimum plus your extra) is subtracted, until the balance clears. The comparison against minimum-only payments comes from running the same loop twice.
Debt accumulates against an 8-hour baseline, the midpoint of the 7–9 hour adult recommendation. Cumulative debt is converted into whole nights lost. Cognitive effects reference the classic dose-response restriction studies.
Calories per unit of activity assume an average adult of about 170 lb (77 kg) at a moderate pace. Weight change uses 3,500 kcal ≈ 1 lb of fat, with a decay factor applied over long horizons to reflect metabolic adaptation.
Daily minutes are converted to cumulative practice hours, then compared against commonly cited hour thresholds for each skill. These are rough consensus figures — practice quality moves them by a factor of two or more.
Hours per day become hours per year (365 days, or 250 for commuting and work scenarios), then get translated into waking days and opportunity cost at a stated hourly rate.
It is not medical, financial, legal or dietary advice, and it cannot account for your individual circumstances. It is a thinking tool: it makes the size of a small daily decision visible. If a simulation prompts a real decision about your health or money, take it to a professional who can see your whole situation.
No. Every figure comes from a deterministic formula written in the source code — compound interest, calorie balance, sleep-debt accumulation, practice-hour thresholds. The same question always returns the same answer, and the assumptions are printed on every page.
They summarise timelines that are widely published by public-health bodies and commonly reported in the research literature (for example, carbon monoxide normalising within 12 hours of the last cigarette). They describe typical patterns, not your individual case.
Because a simulator has to assume something. Savings use a competitive high-yield rate and investing uses a long-run market average. Both are stated on the page, and at 0% return the deposit total is still shown.
It is a useful approximation that overstates long-run change, because energy expenditure adapts as body mass changes. Simulations here show the straight-line figure and an adaptation-adjusted figure side by side.
The simulator has no database and no accounts. What you type is used to route you to a scenario page and nothing else.