Updated May 2026 · 25 Quick Answers
Quick answers to the questions behind the calculators.
Short, formula-first explanations of compound interest, APR, BMI, TDEE, macros, mortgage math, NPV, and the rest of the math that drives our 1,061 free calculators. Every answer is sourced to public authorities — the IRS, SEC, CFPB, CDC, and peer-reviewed research — and links to the calculator that runs the formula.
How Quick Answers Are Written
Each Quick Answer follows the same shape: a one-sentence direct answer, the formula in plain notation, a worked example, and a "when this differs from intuition" section. The format is designed so a reader who needs a fast number gets it in the first paragraph, while a reader who wants to understand the math can keep reading. Every page links to at least one CalcIntel calculator that runs the formula on user-supplied inputs.
Sources and Authority
Finance answers reference the U.S. Internal Revenue Service, the U.S. Securities and Exchange Commission, and the Consumer Financial Protection Bureau — the federal authorities that publish the consumer-facing definitions of APR, mortgage interest, retirement contribution limits, and disclosure rules. Health answers cite peer-reviewed clinical formulas (Mifflin-St Jeor, Harris-Benedict, CDC BMI categories). Spreadsheet answers mirror Microsoft Excel and Google Sheets official function documentation exactly.
How to Read a Quick Answer
Each Quick Answer page is structured for fast scanning. The headline answer is the first sentence. The formula appears in plain notation immediately after, followed by a worked example using realistic numbers. The "where this differs from intuition" section flags the corner cases where naive use of the formula goes wrong — for example, why APR is usually higher than the quoted rate, why daily compounding barely beats monthly compounding over normal time horizons, or why BMI is a poor measure for muscular adults. We close every page with a citation and a link to the calculator that runs the formula.
How Quick Answers Connect to Calculators
Every Quick Answer is paired with at least one CalcIntel calculator. If you read "What is compound interest?", you can immediately open the compound-interest calculator and plug in your own numbers. The connection runs both ways: every calculator page links back to the Quick Answers that explain its formula. This pairing is designed to answer both halves of the user\'s question — "what is this?" and "what does it mean for my numbers?" — without making the reader switch sites or sources.
Update Cadence
Quick Answers are reviewed when their underlying source publishes a revision. When the IRS announces new contribution limits each fall, related answers (401(k), IRA, HSA contribution caps) are refreshed within two weeks. When the CDC issues revised BMI categories, the BMI answers are updated. Spreadsheet answers are reviewed against current Microsoft Excel and Google Sheets documentation each year. The current catalog covers 25 answers across 10 categories and was last refreshed May 2026.
Not Personal Advice
Quick Answers explain how formulas work; they do not know your specific situation. They are educational reference material. For decisions that depend on personal circumstances — tax planning, investment allocation, mortgage approval, clinical assessment, business hiring math — consult a licensed professional. CalcIntel content is published as a public reference and is not intended to substitute for advice from a CPA, registered investment adviser, physician, attorney, or other qualified professional in the relevant field.
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Finance(11)
How is APR calculated?
APR (Annual Percentage Rate) = ((Interest + Fees) / Principal) / Loan Term in Years × 100. It includes the interest rate plus any up-front fees, spread across the life of the loan,…
What is compound interest?
Compound interest is interest that earns interest. Each period, interest is added to the principal, and the next period's interest is calculated on the new, larger balance. Formula…
What is a good debt-to-income ratio?
A DTI under 36% is generally considered good, and most mortgage lenders cap DTI at 43% for qualified loans. Under 20% indicates strong financial health; above 43% makes borrowing d…
How much house can I afford?
The 28/36 rule: spend no more than 28% of gross monthly income on housing and no more than 36% on total debt. For a $100K income, that's about $2,333/month for housing, roughly a $…
What is net present value (NPV)?
NPV is the current value of future cash flows, discounted to today's dollars. NPV = Σ (Cash Flow_t / (1 + r)^t) − initial investment. Positive NPV means the investment beats the di…
How is mortgage interest calculated?
Mortgage interest is calculated monthly on the remaining balance. Formula: monthly interest = (balance × annual rate) / 12. Early payments are mostly interest; late payments are mo…
How do you calculate ROI?
ROI = (Gain − Cost) / Cost × 100. For a $1,000 investment that returns $1,250, ROI = ($250/$1,000) × 100 = 25%. Annualized ROI adjusts for time: ((1 + total ROI)^(1/years) − 1) × 1…
How is a Roth IRA taxed?
Roth IRA contributions are made with after-tax dollars, so they're not deductible. All qualified withdrawals in retirement, including earnings, are 100% tax-free. Contributions can…
How do you pay off credit card debt faster?
Three proven strategies: (1) pay more than the minimum, even $50 extra/month cuts years off; (2) target highest-APR cards first (avalanche method); (3) consolidate to a 0% balance …
What is a good credit utilization ratio?
Credit utilization = current balances / total credit limits. For the best FICO scores, keep utilization below 30% overall, and ideally under 10%. A $10,000 total limit means carryi…
How do you calculate the Sharpe ratio?
Sharpe ratio = (Portfolio Return − Risk-Free Rate) / Portfolio Standard Deviation. It measures return per unit of risk. Above 1 is good, above 2 is very good, above 3 is exceptiona…
Health(6)
What is BMI and how is it calculated?
Body Mass Index (BMI) = weight (kg) / height (m)². In pounds and inches: BMI = (weight × 703) / height². The WHO defines normal weight as 18.5-24.9, overweight as 25-29.9, and obes…
How many calories should I eat per day?
Most adults need 1,600-2,400 calories per day for weight maintenance, depending on sex, age, weight, and activity level. Subtract about 500 calories per day for roughly 1 lb/week w…
What is a healthy body-fat percentage?
For men, 10-20% body fat is generally considered healthy; 21-24% is acceptable; 25%+ is obese. For women, 18-28% is healthy; 29-31% is acceptable; 32%+ is obese. Athletes run leane…
What is TDEE?
TDEE (Total Daily Energy Expenditure) is the total calories your body burns in a day, including resting metabolism, digestion, activity, and exercise. TDEE = BMR × activity multipl…
How much protein should I eat per day?
For most adults, 0.7-1.0 grams of protein per pound of body weight (1.6-2.2 g/kg) is ideal for muscle maintenance and fat loss. Sedentary adults need only 0.36 g/lb (RDA minimum). …
How do you calculate your macros?
Macros = calories split between protein (4 cal/g), carbs (4 cal/g), and fat (9 cal/g). A common split is 40% carbs / 30% protein / 30% fat. On 2,000 calories: 200 g carbs, 150 g pr…
About These Answers
What are CalcIntel Quick Answers?
Quick Answers are short, formula-first explanations of the questions behind common calculators — what APR is, how compound interest actually works, how BMI is computed, what TDEE means, how the 28/36 rule works, and so on. Each answer is paired with one or more calculators so you can move from "what is this?" to "what does it mean for me?" in one step.
Where do the answers come from?
Finance answers cite the U.S. Internal Revenue Service, the SEC Office of Investor Education, and the Consumer Financial Protection Bureau (CFPB). Health answers reference peer-reviewed sources (Mifflin-St Jeor for TDEE, CDC BMI guidance). Spreadsheet answers cite official Microsoft Excel and Google Sheets documentation. Construction answers reference industry standards and trade publications. Every answer page links to its primary source.
Are these answers financial, medical, or legal advice?
No. Quick Answers are educational explanations of formulas and concepts. They are not personalized advice. For decisions that depend on your specific situation — tax planning, investment allocation, medical assessment, real estate purchases — consult a licensed professional in the relevant field.
How often are Quick Answers updated?
Each Quick Answer is reviewed when its underlying source publishes a revision (for example, when the IRS updates contribution limits or the CDC revises BMI guidance). The answer index is refreshed alongside the calculator catalog; the current version was last updated May 2026.
Can I cite a Quick Answer in my own work?
Yes. Each Quick Answer page includes a citation block with the page URL, the underlying source, and the last-modified date. CalcIntel's editorial content is licensed for educational reuse with attribution; the underlying federal data and formulas are public domain.
Sources: U.S. Internal Revenue Service · U.S. Securities and Exchange Commission · Consumer Financial Protection Bureau · Microsoft Excel docs · Google Sheets docs. Last refreshed May 2026. Educational reference only — not personal financial, tax, medical, or legal advice.