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17 calculators for money, dates and everyday life — mortgage payments, compound growth, exact age, working days. Nothing you type is sent anywhere. No account, no pop-ups.
Money
Loans, mortgage, compound interest, savings goals, percentages
Loan calculator
Monthly payment and total interest for fixed-payment, equal-principal and interest-only loans.
Mortgage calculator
Monthly principal & interest plus taxes, insurance and HOA for a home purchase.
Compound interest calculator
How an initial amount plus monthly contributions grows with compounding.
Savings goal calculator
How long it takes to reach a target with monthly saving and a return rate.
Percentage calculator
Percent of a number, percent change, increase and discount — without the confusion.
Tip calculator
Tip amount, total and per-person split.
Dates
Age, countdowns, working days, weekday, time zones
Age calculator
Exact age in years, months and days, plus days until your next birthday.
Date difference & countdown
Days between two dates, countdown to a date, and years/months/days breakdown.
Working days calculator
Business days between two dates, excluding weekends and holidays.
Day of the week
Which weekday a date falls on, plus day-of-year and week number.
Time zone converter
Convert a time between cities, with daylight saving handled automatically.
Everyday
BMI, calories, unit conversion, random picks
BMI calculator
Body mass index and the normal weight range for your height.
Calorie & BMR calculator
Basal metabolic rate and daily calorie needs by activity level.
Unit converter
Length, weight, area, volume and temperature — metric, imperial and East Asian units.
Random pairing (ladder draw)
Randomly pair participants with outcomes — who buys coffee, who goes first.
Random picker
Pick one option at random.
Team generator
Randomly split people into evenly sized teams.
Practical guides
How to read the result and what to decide with it.
- How mortgage payments are calculated — and why the first years are almost all interest
- Compound interest explained with real numbers — why starting 10 years earlier doubles the result
- Loan amortization schedule explained — reading the table and using it to pay off debt faster
- Percentage change vs percentage points — the mistake that makes headlines wrong
- BMI: what the number means, where the categories come from, and what it misses
- How to count working days correctly for deadlines, deliveries and leave
Are the results accurate?
NumSmith implements the standard formulas and published rates exactly, and each calculator shows the year its rates are based on. Taxes and insurance still depend on personal circumstances, so treat results as estimates and confirm final figures with your lender, employer or tax authority.