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Tools & Calculators
Fast, accurate tools and calculators for finance, math, health, IT, and more. Instant results with no sign-up required.
About Calc Hammer
Calc Hammer is a free library of calculators and practical online tools built for people who need a clear answer, fast. Whether you are refinancing a mortgage, sizing a concrete slab, working out a healthy calorie target, or decoding a JWT during a debugging session at 2 a.m., we want you to land on a page, get the number, and move on.
Every calculator on this site does three things: it shows the underlying formula, walks through a real-world example, and lists the assumptions used so you can sanity-check the result yourself. That matters because a number on its own is only as useful as the context around it — a "good" mortgage rate in 2026 is not the same as one in 2021, and a BMI of 26 means something different for a 25-year-old strength athlete than for a sedentary 60-year-old.
We do not ask for an email address, we do not gate features behind a sign-up, and we do not sell what you type in. Most calculators run entirely in your browser, so the numbers you enter never leave your device. The only third-party scripts we load are analytics and advertising, both gated behind a cookie-consent banner that you can decline at any time without losing functionality.
Calc Hammer is built and maintained by a small independent team. If a calculator gives you a result that seems off, or you would like one that does not exist yet, the contact link in the footer goes straight to a real inbox.
Popular Calculators
Mortgage Calculator
Calculate your monthly mortgage payment and total interest.
BMI Calculator
Calculate your Body Mass Index and find your weight category.
Percentage Calculator
Calculate percentages, percentage change, and more.
Compound Interest Calculator
See how your money grows over time with compound interest.
Loan Calculator
Calculate monthly payments and total cost for any loan.
Calorie Calculator
Estimate your daily calorie needs based on your profile.
Featured Guides
Specialized calculators with worked examples
How Much House on $100k Salary?
What a six-figure salary actually buys in 2026 mortgage terms — with example DTI and down-payment math.
Mortgage Refinance Savings
Compare your current loan against today's rate and see whether refinancing actually pays back.
Calories to Lose Weight
A practical, science-grounded target — not the generic 'eat less, move more.'
Compound Interest + Contributions
See how regular monthly deposits compound alongside a starting balance.
Fuel Cost Per Mile
Calculate the true per-mile fuel cost of a trip given price and MPG.
Concrete Slab Calculator
Get the exact cubic yards/meters for a slab pour, with waste-factor adjustment.
Trending Calculators
Based on community ratings
Mortgage Calculator
Calculate your monthly mortgage payment, total interest, and total cost of your home loan.
Compound Interest Calculator
See how your money grows over time with the power of compound interest.
Loan Calculator
Calculate monthly payments, total interest, and payoff date for any loan.
Investment Calculator
Project the future value of your investments with regular contributions.
Retirement Calculator
Plan your retirement savings and estimate your monthly retirement income.
Pension Calculator
Project your pension pot and monthly retirement income with inflation adjustments in today's money.
Finance Calculators
Mortgage Calculator
Calculate your monthly mortgage payment, total interest, and total cost of your home loan.
Compound Interest Calculator
See how your money grows over time with the power of compound interest.
Loan Calculator
Calculate monthly payments, total interest, and payoff date for any loan.
Math Calculators
Scientific Calculator
Full scientific calculator with trigonometry, logarithms, exponents, factorials, memory, and degree/radian modes.
Percentage Calculator
Calculate percentages, percentage change, and percentage of a number.
Fraction Calculator
Add, subtract, multiply, and divide fractions with step-by-step solutions.
Physics Calculators
Health Calculators
Construction Calculators
Everyday Calculators
IT Tools
UUID Generator
Generate cryptographically secure UUID v4 identifiers.
JSON Formatter
Format, validate, and beautify JSON data.
JWT Decoder
Decode JWT tokens to view header, payload, and expiration.
Hash Generator
Generate SHA-256, SHA-512, and MD5 hash digests.
Cron Expression Parser
Parse cron expressions into human-readable schedules.
CIDR/Subnet Calculator
Calculate network address, subnet mask, and usable hosts.
Latest Articles
The Rule of 72 is wrong. Here's why that's fine, and the exact rule when it isn't.
The Rule of 72 says your money doubles in 72/r years at r% interest. It's a near-miss approximation, accurate at one specific rate and slightly off everywhere else. Here's the exact derivation and the corrections that matter.
15-Year vs 30-Year Mortgage: Which Saves You More?
Compare the true cost of a 15-year and 30-year mortgage to find out which loan term saves you the most money over time.
How to Calculate Your Monthly Mortgage Payment (Step by Step)
Learn the exact formula lenders use to calculate your monthly mortgage payment, with a step-by-step walkthrough and real examples.
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