Everyday Life calculators
Age, tips, date spans, fuel costs — the numbers daily life asks for. Every tool shows its formula, updates live, and works on any device.
Saved & recent
- Age CalculatorExact age in years, months, and days on any reference date — plus totals in months, weeks, days, and hours, your birth weekday, and a next-birthday countdown.→
- Date & Time CalculatorOne page for everyday date and time math: add or subtract days, weeks, months or years, days until or since a date, day of week, day of year, ISO 8601 week number, leap years, Monday–Friday work days, clock-time spans, time-card hours, and Unix timestamps.→
- Days Between Dates CalculatorTotal days between two dates — calendar or business days, with or without the end date counted — plus weeks-and-days and years-months-days breakdowns.→
- Fuel Cost CalculatorTrip fuel cost from distance, MPG, and gas price: gallons burned, cost per mile, cost per 100 miles, and the L/100km equivalent — all worked out.→
- Pet & Aquarium CalculatorTwelve husbandry calculations in one dropdown: aquarium volume in gallons and liters, the one-inch-per-gallon stocking check, heater wattage, substrate pounds, terrarium sizes by species, dog crate dimensions, chicken coop and run square footage, eggs and feed per flock, the cats-plus-one litter rule, hay by percent of body weight, and daily walk time by breed group. Every answer is a published rule of thumb with its formula and caveats shown — confirm the big decisions with a vet, a fish shop, or a care sheet.→
- Pet Care CalculatorDog and cat ages in human years, diphenhydramine reference doses by weight, daily calorie targets from the RER formula, food portions in cups, and daily water intake — one dropdown for the published pet reference ranges. Every number is a reference to confirm with your veterinarian, not an instruction.→
- Time to Decimal CalculatorConvert hours:minutes:seconds into decimal hours for timesheets and payroll — exact or rounded to 0.01, 0.1, or 0.25 h — with the reverse conversion checked.→
- Tip CalculatorTip amount, bill total, and each person’s share from the pre-tax bill, any tip percentage, and the party size — with the arithmetic shown line by line.→
How this manual is organized
Each entry above opens a one-page tool: inputs on the left, the live result on its color board, and beneath the card the formula with worked examples and the method's limits. Save the tools you use often — they'll wait on this shelf next visit.