Everyday Life Calculators

Standard US tipping: Restaurants: 15-20% (20% is new standard). Exceptional service: 20-25%. Poor service: 10-15% (still tip something unless truly egregious). Food delivery: 15-20% or $5 minimum. Bartender: $1-2 per drink or 15-20% tab. Coffee shop: $1-2 or 15-20% on complex orders. Hairstylist: 15-20%. Taxi/rideshare: 15-20%. Hotel housekeeping: $2-5 per night. Tip on pre-tax amount. Calculate: Move decimal left one space, double it for 20%. Our tip calculator handles split bills and custom percentages.

Monthly payment formula: M = P[r(1+r)^n]/[(1+r)^n-1]. P = principal, r = monthly rate (annual/12), n = months. Example: $300k loan, 6% APR, 30 years. r = 0.06/12 = 0.005. n = 360. Payment = $1,799/month. Total paid = $647,515 (interest = $347,515). 15-year loan same rate = $2,532/month but total $455,760 (save $191k interest). Payment includes principal + interest. Add insurance, taxes, HOA for total housing cost. Our mortgage calculator shows amortization schedule and compares different loan terms.

28/36 rule: Housing costs ≤28% gross monthly income. Total debt ≤36% gross income. Example: $5,000/month income. Max housing = $1,400 (including mortgage, insurance, taxes, HOA). Max total debt = $1,800 (housing + car, credit cards, student loans). Assuming 6% mortgage, 30 years, $300/month taxes+insurance = $1,100 for mortgage = ~$183k house price. Lenders may approve more, but stick to 28/36 rule for financial comfort. Include down payment, closing costs, emergency fund in planning.

Count hours difference between zones. US: Pacific +3 hours = Eastern. Example: 2pm Pacific = 5pm Eastern. International: Use UTC offset. Pacific is UTC-8 (winter) or UTC-7 (summer DST). London is UTC+0. Singapore is UTC+8. 9am Pacific = 5pm London (8 hours ahead) = 1am next day Singapore (16 hours ahead). Remember Daylight Saving Time changes (spring forward, fall back). Use world clock or our time zone calculator to avoid confusion, especially for meetings and travel.

General rule: 3-6 months of expenses. Single income or variable income: 6-9 months. Dual stable incomes: 3-4 months. Self-employed: 6-12 months. Example: $3,500/month expenses × 6 = $21,000 emergency fund. Keep in high-yield savings account (not checking or investments). Build gradually: start with $1,000 minimum, then aim for one month, work up to full goal. Don't touch except true emergencies (job loss, medical crisis, essential home repairs). Separate from other savings goals.

50/30/20 budget rule: 50% Needs (housing, utilities, groceries, insurance, minimum debt payments). 30% Wants (dining out, entertainment, hobbies, subscriptions). 20% Savings (retirement, emergency fund, debt payoff above minimums). Example: $5,000/month take-home. Needs = $2,500, Wants = $1,500, Savings = $1,000. Adjust percentages based on situation: high cost of living may push needs to 60%. Aggressive debt payoff or FIRE pursuit may flip to 50/20/30. Track actual spending, adjust categories monthly.

Include all costs: Gas ($0.12-$0.20/mile), Maintenance ($0.09/mile average), Tires ($0.03/mile), Insurance (annual cost ÷ miles driven), Registration (annual ÷ miles), Depreciation ($0.20-$0.40/mile). Total: $0.50-$0.80 per mile typically. IRS mileage rate (2024): $0.67/mile business, $0.21 medical/moving. Example: 12,000 miles/year. $2,000 gas + $1,000 maintenance + $1,500 insurance + $1,500 depreciation = $6,000 ÷ 12,000 = $0.50/mile. Use this for reimbursement, cost comparisons, budgeting.

Popular myth: 21 days. Research shows: 18-254 days, average 66 days for a behavior to become automatic. Depends on habit complexity, person, environment. Simple habits (drinking water) faster than complex (daily exercise). Building new habits is easier than breaking old ones. Strategies: Replace habit with alternative behavior, change environment triggers, track daily streaks, start tiny (2-min version), use implementation intentions ('If X, then Y'). Missing one day doesn't reset progress. Consistency matters more than perfection.