Guides that explain what the tool is doing
Each guide starts with a tool you already use, then shows what happens under the hood with real numbers.
Page 4 of 5Binary, hex and decimal: counting in bases 2, 10 and 16
Computers store everything as bits, but people read decimal, and programmers often use hexadecimal as a shortcut. The same number, 202, is 11001010 in binary and CA in hex. This guide shows how to convert between them by hand, why one hex digit equals four bits, and where you meet these systems every day.
Electricity Cost CalculatorWhat your appliances cost per month: watts, hours and units explained
Your bill is a count of units, and one unit is one kilowatt-hour. A 1.5-ton AC running 8 hours a day uses about 288 units a month, which at ₹8 a unit is ₹2,304. A ceiling fan for 10 hours costs ₹168. This guide shows the formula and which appliances really drive the bill.
Investment Growth CalculatorStart at 25 or 35? What waiting ten years really costs
Ravi invests ₹5,000 a month from age 25 to 35, then stops. Meera starts at 35 and keeps going until 60. At 12% a year, Ravi ends with ₹2.30 crore and Meera with ₹95 lakh, even though Meera put in 2.5 times more money. Here is the whole picture, year by year.
Markup & Margin CalculatorMarkup vs margin: why a 50% markup is only a 33% margin
Markup is profit as a share of cost. Margin is profit as a share of the selling price. A product that costs ₹600 and sells for ₹1,000 has a 66.7% markup and a 40% margin. Mixing the two up quietly cuts your profit, and this guide shows exactly how.
HRA Exemption CalculatorHRA exemption: the least of three rules, with a worked example
The tax-free part of your House Rent Allowance is the smallest of three numbers: the HRA you actually get, a share of your basic salary, and the rent you pay minus 10% of your basic. With ₹40,000 basic, ₹20,000 HRA and ₹18,000 rent in a metro, ₹14,000 a month is exempt. Here is why, and how to improve it.
Break-Even CalculatorBreak-even point: how many sales before you make a profit
Break-even is the number of units you must sell before income covers all your costs. With ₹60,000 of fixed costs, a ₹500 price and ₹300 of variable cost per unit, you break even at exactly 300 units, which is ₹1,50,000 of sales. This guide shows the formula, the graph and five ways to move the point.
Heart Rate Zone CalculatorHeart rate zones explained: what each of the five zones is for
Training zones split your effort into five bands, from easy walking to an all-out sprint. For a 30-year-old with an estimated maximum of 190 beats a minute, the bands run from 95 to 190. This guide shows how the zones are worked out, what each one feels like and how to spread your week across them.
IP Subnet CalculatorCIDR and subnets: what /24, /26 and /20 really mean
The number after the slash in an address like 192.168.1.0/24 counts how many of the 32 bits belong to the network. The rest are for hosts. A /24 holds 256 addresses, a /26 holds 64 and a /20 holds 4,096. This guide shows how to read, split and size a subnet.
PPF CalculatorPPF in pictures: ₹1.5 lakh a year for 15 years, and why the last years do the heavy lifting
Put the maximum into a PPF every year and you invest ₹22.5 lakh over 15 years. At 7.1 percent you end with about ₹40.7 lakh. More than ₹18 lakh of that is interest, and most of it arrives in the final years.
FD CalculatorA 7% fixed deposit: what is left after tax and inflation
A ₹10 lakh FD at 7 percent shows ₹14 lakh after five years. After 30 percent tax on the interest it is ₹12.7 lakh. After 6 percent inflation, it buys what ₹9.5 lakh buys today. The deposit is safe. The purchasing power is not.
Percentage CalculatorPercent vs percentage points: the difference behind half the misleading headlines
The interest rate rose from 5 percent to 8 percent. Is that a 3 percent rise or a 60 percent rise? Both are true, and they mean very different things. Here is how to tell them apart in ten seconds.
HTTP Status Code LookupHTTP status codes: the five families, and the dozen you will actually meet
Nobody needs to memorise sixty codes. Learn the five families by their first digit and a dozen common ones, and you can read almost any error message, API response or browser warning.
PX to REM Converterpx vs rem: why your font sizes should be allowed to scale
Pixels are fixed. Rem units follow the reader's own text size. The switch takes one division by 16, and it quietly makes your site usable for everyone who has changed their browser's font size.
Cron Expression ExplainerReading a cron expression: five fields and six gotchas
“0 9 * * 1-5” looks like noise. It means 9:00 every weekday. Once you can read the five fields left to right, you can schedule a backup, a report or a reminder in a single line.
JWT DecoderInside a JWT: three parts, two dots, and why decoding is not the same as trusting
A JSON Web Token looks like a random string with two dots. Split it at the dots and each part is readable. The catch: anyone can read it, and only the signature proves nobody changed it.
Gratuity CalculatorThe gratuity formula (15/26): what your years of service are worth
Gratuity is a lump sum paid when you leave a job after five years. The formula is last salary × 15 ÷ 26 × years. At ₹50,000 a month, ten years is about ₹2.88 lakh. Here is where the 26 comes from and what to watch.
Step-Up SIP CalculatorStep-up SIP: raise your SIP 10 percent a year and almost double the result
A flat ₹10,000 SIP and one that grows 10 percent a year start in exactly the same place. Twenty years later, one has ₹1 crore and the other nearly ₹2 crore. Here is why a small yearly raise does so much.
Loan Prepayment Calculator (Interest Saved)One extra EMI a year: how a 20-year home loan quietly becomes a 17-year loan
Pay a single extra EMI every year on a ₹50 lakh loan and you finish about 3 years early and save more than ₹10 lakh in interest. Here is exactly why prepayment works so well, and when it does not.
Password Entropy CalculatorPassword entropy: what “bits” really mean, and why length beats symbols
An 8-character password with every symbol on the keyboard falls in days. A six-word passphrase of plain lowercase words outlasts the age of the universe. The difference is a number called entropy, and it is easy to read once you see it drawn.
FIRE Calculator (Financial Independence Number)The 25x rule: how much money is “enough” to stop working
Multiply what you spend in a year by 25 and you get a first estimate of the savings that could pay for it. The rule is simple, famous and a little too optimistic for India. Here is how to use it honestly.
Discount Calculator50% off plus 20% off is not 70% off: how stacked discounts really work
A sale says “extra 20% off already reduced prices”. Your brain adds the two numbers. The shop does not. The real answer is 60 percent, and the gap gets wider the bigger the discounts get.
Readability Score CheckerFlesch reading ease: what your readability score really means
A score of 60 to 70 is “plain English”. A score of 30 is a legal contract. The formula behind it looks at only two things, sentence length and word length, which makes it easy to improve once you see how it works.
Sleep Cycle CalculatorSleep in 90-minute cycles: when to go to bed so the alarm does not feel like an attack
You do not wake up groggy only because you slept too little. Often it is because the alarm cut into the middle of a deep cycle. Counting back in blocks of about 90 minutes is a simple way to plan your night.
UUID GeneratorCan two UUIDs ever be the same? The odds, in pictures
A random UUID has 122 random bits, a number with 37 digits. You could generate a billion of them every second for 86 years before a clash became as likely as a coin flip. Here is what that means for real systems.
Emergency Fund CalculatorHow big should an emergency fund be? A simple way to pick your number
Three months, six months, twelve months: everyone has an opinion. The right answer depends on three things about your life, and you can work it out in two minutes with your own monthly spending.
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