Guides
Our calculators give you a number. These guides explain where the number comes from, which rules apply, and how to act on it — with worked examples you can check line by line.
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India tax & salaryOld vs New Tax Regime (FY 2025-26): Which One Saves You More?For FY 2025-26 the new regime wins for almost everyone, because a salaried person pays zero tax up to ₹12.75 lakh gross. The old regime only overtakes it once your provable deductions cross roughly ₹5.4 lakh at ₹15 lakh income, rising to a flat ₹8 lakh above ₹25 lakh.8 min read · Reviewed 26 July 2026India tax & salaryGST 2.0 Slabs Explained: What Changed in September 2025From 22 September 2025 India’s four main GST slabs became two: 5% and 18%, with a 40% demerit rate on a short list of sin and luxury goods. Most 12% items dropped to 5% and most 28% items to 18%. The old slabs still matter for reading older invoices.8 min read · Reviewed 26 July 2026India tax & salaryHRA Exemption: How to Calculate It Correctly (and When It’s Worthless)Your HRA exemption is the least of three figures: the HRA you actually received, 50% of basic plus DA in a metro (40% elsewhere), and rent paid minus 10% of basic plus DA. The third limb almost always decides it — and under the new tax regime the exemption is zero regardless.8 min read · Reviewed 26 July 2026
India tax & salary
- Old vs New Tax Regime (FY 2025-26): Which One Saves You More?A worked comparison of India’s old and new income tax regimes for FY 2025-26, including the deduction level at which the old regime starts winning.8 min read
- GST 2.0 Slabs Explained: What Changed in September 2025India’s GST slabs collapsed into 5% and 18% with a 40% demerit rate from 22 September 2025. Here is what moved, what became exempt, and how to read an invoice.8 min read
- HRA Exemption: How to Calculate It Correctly (and When It’s Worthless)The three-limb HRA exemption rule explained with a worked example, metro vs non-metro rates, landlord PAN rules, and why the new regime removes the benefit entirely.8 min read
- CTC vs Take-Home Salary: Where Your Package Actually GoesWhy a ₹12 lakh CTC never lands ₹1 lakh a month in your account — a component-by-component breakdown of basic, HRA, PF, gratuity, professional tax and income tax.8 min read
Saving & investing
- PPF vs EPF vs NPS: Choosing a Retirement Account in IndiaLock-in, returns, tax treatment and withdrawal rules for PPF, EPF and NPS compared side by side, with the corpus each builds on the same monthly contribution.10 min read
- SIP vs Lumpsum: Which Builds More Wealth?The maths behind rupee-cost averaging versus investing a lump sum, when each wins, and why the honest answer depends on cash flow rather than market timing.10 min read
- FD vs RD: Which Deposit Fits Your Goal?Fixed and recurring deposits compared on compounding, effective yield, liquidity and TDS — plus why an RD at the same rate earns far less than an FD.10 min read
- Compound Interest Explained With Real NumbersHow compounding frequency, contribution timing and time horizon change the outcome — including why starting ten years earlier beats contributing twice as much.9 min read
Loans & mortgages
- How Home Loan EMI Works — and Four Ways to Cut Total InterestThe amortisation maths behind your EMI, why early payments are almost all interest, and what prepayment, tenure choice and rate resets actually save.9 min read
- APR vs Interest Rate: What Lenders Don’t Spell OutWhy two loans at the same headline rate can cost thousands apart — fees, flat vs reducing balance, and how to compare offers on a single honest number.8 min read
- How Much House Can You Afford? The 28/36 Rule, Honestly AppliedWhat the 28/36 debt-to-income guideline includes, the costs buyers forget (taxes, insurance, PMI, maintenance), and how a rate change moves your budget.9 min read
- Should You Refinance? Run the Break-Even Math FirstThe one calculation that decides a refinance: closing costs divided by monthly saving. Plus the traps — resetting the term, cash-out creep and rate-lock timing.9 min read
Health & fitness
- BMI: What It Actually Tells You (and What It Misses)Why a screening number invented for populations misjudges athletes and older adults, what the WHO cutoffs mean, and which measurements add real information.9 min read
- TDEE and Calorie Targets: A Practical GuideHow BMR, activity multipliers and exercise combine into a daily calorie number, how to set a sane deficit or surplus, and why the scale lies for two weeks.9 min read
Files & privacy
- Compress Images Without Wrecking Quality: JPG vs PNG vs WebPWhich format to use for photos, screenshots and logos, what a quality slider really does to your pixels, and how to hit a page-weight budget without visible loss.9 min read
- The Location Data Hidden in Your PhotosEvery phone photo can carry GPS coordinates, timestamps and device serials. Here is what EXIF stores, which platforms strip it, and how to remove it before sharing.9 min read
How we write these guides
Every formula in a guide is the same formula our calculators run, and every worked example is checked against the code before publishing. Time-sensitive figures — tax slabs, statutory rates, thresholds — carry the year they apply to, and finance and health guidance is written as information rather than advice. Read more about how ZoolTools builds and tests its tools.