10 guides
Guides and tips
Clear, worked explanations of the maths behind loans, taxes, investing, health numbers, grades and online selling, each with a calculator to try your own figures.
Maths basicsHow to Calculate Percentage Increase and Decrease (and the 20% Trap)Work out percentage increase and decrease in three steps, see why a 20% rise followed by a 20% fall does not bring you back, and avoid common mistakes.
Home loansHome Loan Prepayment: Should You Reduce the EMI or the Tenure?A ₹2 lakh prepayment on a ₹30 lakh home loan saves ₹5.6 lakh if you cut the tenure, but only ₹1.8 lakh if you cut the EMI. Here is why, with the numbers.
HealthIdeal Weight for Your Height: What the Four Formulas SayHow the Devine, Robinson, Miller and Hamwi formulas estimate ideal body weight, worked examples for men and women, and why a healthy range matters more.
StudentsAttendance Percentage: How Many Classes Can You Miss Under the 75% Rule?Calculate your attendance percentage, how many classes you must attend in a row to reach 75%, and how many you can still miss this term, with clear examples.
DatesHow to Calculate Your Exact Age in Years, Months and DaysCalculate exact age by hand, handle month lengths and leap years, see how birthdays on 29 February work, and convert age into total days, weeks and months.
HomeHow Your Electricity Bill Is Calculated: Units, Slabs and ChargesUnderstand your electricity bill: what a unit is, how slab tariffs work, fixed charges and duty, with a worked 320-unit example and tips to cut the bill.
Online sellingROAS vs ROI: Which Number Tells You if Your Ads Make Money?ROAS and ROI measure different things. See both formulas, a worked ad campaign example, the break-even ROAS for your margin and which number to use when.
ShoppingWhy 20% + 10% Off Is Not 30% Off: Stacked Discounts ExplainedLearn how stacked discounts really work, why 20% then 10% off equals 28%, how to compare sale offers, and how to work out the real percentage off any price.
Home projectsHow Much Paint Do I Need? Room Calculation With a Worked ExampleWork out how much paint a room needs: measure walls, subtract doors and windows, allow for coats and coverage, with a worked example and buying tips.
Money basicsInflation: What Will ₹1 Lakh Be Worth in 20 Years?See how inflation erodes money over time: what ₹1 lakh of today’s spending will cost in 20 years, what ₹1 lakh will buy then, and how to plan goals for it.