Transparent calculations
Methodology
CostsPerDay calculators are deterministic: the same inputs produce the same outputs. All calculations are performed locally in the browser.
Shared conventions
Unless a calculator states otherwise, a year is 365 days, a week is 7 days and annual weekly amounts use 52 weeks. Average monthly values use annual value ÷ 12. These conventions are deliberately simple and may not match every calendar year or billing contract.
Displayed currencies are rounded for readability, normally to two decimal places. Internal calculations use JavaScript numeric precision before display rounding.
Daily expense calculator
Daily expense = total annual expenses ÷ 365
Average month = annual expenses ÷ 12
Frequency factors are 365 for daily, 52 for weekly, 12 for monthly and 1 for annual amounts.
Cost per day
Months are converted with 365 ÷ 12 average days; years use 365 days.
Cost per use
Cost per use = net cost ÷ expected uses
When usage is estimated from a schedule, expected use days = years × 365 × days-used-per-week ÷ 7.
Cost per wear
Cost per wear = net lifetime cost ÷ expected wears
Cleaning can be entered either as a per-wear variable cost or a total lifetime amount. A target cost per wear is supplied by the user, not by CostsPerDay.
Subscription cost
Cost per use = annual plan cost ÷ annual uses
Unused-day cost treats one reported use as one used day, capped at 365 days. That estimate is less informative when multiple uses occur on the same day.
True hourly wage
True hourly wage = (annual pay − annual work costs) ÷ (annual paid hours + annual extra work time)
Extra work time includes weekly unpaid overtime and preparation time plus commuting time per workday multiplied by workdays per week. The calculator does not model taxes, benefits or employment law.
Work hours cost
When monthly pay is supplied, the calculator estimates monthly hours from hours per day × workdays per week × 52 ÷ 12.
Compare cost per use
Cost per use = ownership cost ÷ expected uses
Total-use input overrides the weekly-use estimate when it is above zero.
Residual value and recurring costs
Expected resale or residual value is subtracted where the calculator includes it. Recurring costs are only included where explicitly requested by the calculator and are annualized or extended over the selected lifespan as shown above.
Limitations
Outputs are estimates, not forecasts. Inflation, financing, tax, opportunity cost, changing usage, unexpected repairs and calendar differences can make real-world outcomes differ. The quality of a result therefore depends heavily on the assumptions entered by the user.