Principal (P) — This is the actual amount of money you're borrowing. If you're buying a $30,000 car and putting $5,000 down, your principal is $25,000.

Interest Rate — The yearly cost the lender charges you to borrow. A 6% annual rate means roughly 0.5% per month gets added to your balance.

Loan Term — How long you have to pay it back. Longer terms mean lower monthly payments but way more total interest paid.

Monthly Payment — This is what leaves your bank account every month. It includes both principal repayment and interest.

Total Interest — This is the true cost of borrowing. On a $25,000 loan at 6.5% for 5 years, you'll pay about $4,300 extra just in interest.

Total Cost — Principal + all interest. This is the real number you should compare when shopping loans.

Rate matters most. Even 1% lower rate on a $30,000 loan saves ~$900 over 5 years. Always shop multiple lenders.

Shorter = cheaper overall. A 3-year loan has higher monthly payments than a 5-year loan, but you'll pay significantly less total interest.

Extra payments crush debt. Making one extra payment per year on a 30-year mortgage can cut 4–6 years off the loan.

Watch for prepayment penalties. Some lenders charge fees if you pay off early — always check before making extra payments.

Compound interest means you earn interest on both your original principal and the interest already accumulated. The longer you invest, the more dramatic the effect.

A quick mental math shortcut: divide 72 by your annual interest rate to find how many years it takes to double your money.

At 7%, money doubles every ~10.3 years.
At 10%, money doubles every ~7.2 years.
At 12%, money doubles every ~6 years.

The more frequently interest compounds, the faster your money grows — though the difference shrinks at high frequencies.

Daily compounding grows slightly faster than monthly, which grows faster than quarterly, which grows faster than yearly. For most savings accounts, monthly or daily is standard.

Time is the most powerful variable in the compound interest formula. $5,000 invested at 7% for 30 years grows to ~$38,000. The same amount for 40 years grows to ~$75,000. Ten extra years nearly doubles the outcome.

This tool converts any salary amount to all common pay periods using standard work year assumptions: 52 weeks per year, and the hours per week you specify.

When comparing two job offers with different pay structures, always convert both to the same period. A $45/hr contractor vs a $85,000/yr salaried role — which is better? It depends on hours worked and benefits.

This tool makes that comparison instant.

• Always negotiate annual salary, not hourly. A $2/hr raise sounds small but equals $4,160/year.

• Know your market rate before any negotiation — use this to back-calculate what you should be asking for.

• Factor in benefits, PTO, and remote work when comparing total compensation.

Remember these figures are pre-tax. Depending on your tax bracket, state, and deductions, your actual take-home pay will be lower. As a rough estimate, most people take home 65–75% of their gross salary after federal and state taxes.

To find X% of Y, multiply Y by X divided by 100. The result is the portion that X% represents of the whole.

Shopping discounts — "30% off $85" = $25.50 savings.

Tip calculation — 18% of $60 bill = $10.80 tip.

Grade scores — Got 43 out of 50? That's 86%.

Tax — 8.5% sales tax on $120 = $10.20.

To find how much something increased or decreased in percentage terms:

% Change = ((New − Old) ÷ Old) × 100

Example: Price went from $80 to $100. Change = ((100−80)÷80)×100 = 25% increase.

• 10% — just move the decimal left one place. 10% of $340 = $34.

• 5% — find 10% and halve it.

• 15% — find 10%, add half of that.

• 20% — find 10% and double it.

Tip is calculated as a percentage of the pre-tax bill total. The total is then divided equally between the number of people splitting.

10–12% — Below average or poor service.

15% — Standard, average service.

18–20% — Good service, most common choice.

20–25% — Excellent service.

25%+ — Exceptional, going above and beyond.

Many restaurants add an automatic 18–20% gratuity for groups of 6 or more. Always check your bill before adding an additional tip — you don't want to double-tip by accident.

Hair/nail salon — 15–20%
Food delivery — 10–15% minimum
Taxi/rideshare — 15–20%
Hotel housekeeping — $2–5/night
Bartenders — $1–2/drink or 15–20%

The calculator finds the absolute difference between two dates in milliseconds, then converts to days, weeks, and months.

Project planning — How many business days until the deadline?

Countdown — Days until a vacation, birthday, or event.

Age in days — Use with the Age Calculator to find your total days lived.

Contracts — Count notice periods or contract durations.

Business days are Monday through Friday, excluding weekends. They do not account for public holidays, which vary by country and region. For exact business day counts including holidays, check with your local calendar.

There are exactly 365 days in a regular year and 366 in a leap year. A decade is 3,652–3,653 days. The average human life of 75 years is roughly 27,394 days.

BMI uses your weight and height to estimate body fat. The US formula uses pounds and inches.

Below 18.5 — Underweight

18.5 – 24.9 — Normal weight

25.0 – 29.9 — Overweight

30.0 and above — Obese

BMI is a screening tool, not a diagnostic measure. It doesn't account for:

• Muscle mass — athletes often have high BMI despite low body fat
• Age and gender differences in body composition
• Where fat is distributed in the body
• Bone density

A BMI between 18.5 and 24.9 is generally considered healthy for most adults. However, what's healthy varies by individual. Waist circumference and body fat percentage are often better indicators of health risk than BMI alone.

The calculator finds the exact difference between your date of birth and today (or any chosen date), accounting for varying month lengths and leap years.

The calculator accounts for leap years automatically. A leap year occurs every 4 years (with exceptions for century years not divisible by 400). This ensures your exact day count is always accurate.

10,000 days — About 27 years, 4 months

1 billion seconds — About 31.7 years old

20,000 days — About 54 years, 9 months

100 years — 36,524 or 36,525 days

Legal documents — Verify age eligibility precisely.

Medical — Pediatric care often needs exact age in months.

Curiosity — Find out how many days you've been alive and celebrate milestones like 10,000 days.