About SD.gy
Free, fast, privacy-focused calculators for the math you actually do in real life.
Our Story
SD.gy started in 2024 because the team kept catching themselves googling the same calculations on their phones — split a dinner bill three ways, figure out a child's age in months for a doctor's form, convert a US recipe's cups to grams, work out the BMI my doctor mentioned in passing.
Every result on Google was either an answer-box that gave you a number with no working, or a website wrapped in five layers of pop-ups, app installs, and "for the full breakdown please…" upsells. We wanted somewhere to land, tap five fields, see the answer, and close the tab. Mobile-first because most of these questions happen on a phone, in a hurry.
We launched with the eight calculators we used most ourselves. We add a calculator only when at least two of us notice we are wishing for it. Today the site has more than 18 calculators across math, health, finance, time, and conversions, and every one of them runs entirely in your browser. Your weight, salary, and date inputs never reach our servers — there is nothing to leak.
Display advertising pays for hosting and writing. Ad density stays well below the industry average and ads are never placed between an input and its result. If an ad ever made a calculator harder to use, we move or remove it.
Our Mission
SD.gy exists to give working people a fast, friction-free toolbox for the everyday calculators they actually need every day. We believe everyday utilities should be free, accurate, fast, mobile-friendly, and respect your privacy by default. Whether you are at your desk, on a train, or in a parking lot trying to settle a dinner bill, we want you to find your answer in seconds.
We measure success in three numbers: time-to-answer (target: under 3 seconds from cold load to result), inputs-to-answer (target: as few as possible), and bytes-of-your-data-on-our-servers (target: zero). Everything else is downstream of those numbers.
Long-term, our mission is broader than the current tool catalogue. We want SD.gy to be the place a friend recommends when you say "is there a calculator for that?" — and have you not feel a flicker of regret when you click the link.
Who We Are
SD.gy is operated by SDK Co., Ltd., a Korean software company founded in 2024 that builds developer-focused tools and free online utilities. Our team has shipped consumer and developer web products used by millions, and we apply that same attention to UX, accuracy, and speed to every calculator on this site.
Beyond SD.gy, the same team operates JavaScript.ac (interactive JavaScript learning), SDK.is (developer utilities), SDK.bz (financial and crypto calculators), and SD.gy (everyday calculators). Lessons learned on one site — accessibility patterns, performance budgets, ad-density thresholds — get applied across all of them.
- Company
- SDK Co., Ltd.
- Founded
- 2024
- Focus
- Developer tools, calculators, free utilities
- Business Registration
- 871-81-03242
- E-Commerce Registration
- 2024-고양일산서-1820
- Address
- 4F, 127 Namseong-ro, Jeju-si, Jeju Special Self-Governing Province, Republic of Korea
What You'll Find on SD.gy
SD.gy ships 18+ everyday calculators today, all free, all running 100% in your browser.
Basic Calculator
Standard arithmetic with calculation history and keyboard support. Useful when you do not want to leave the browser tab.
Percentage Calculator
Compute percentages, discounts, percentage changes, and tip splits with a single tap.
Unit Converter
Length, weight, temperature, area, volume, speed, and energy. Supports both metric and imperial.
Date Calculator
Compute D-day, the difference between two dates, and add or subtract days, months, or years.
Age Calculator
Exact age from birthdate in years, months, weeks, and days. Useful for forms and visa applications.
BMI Calculator
Body Mass Index with health-range guidance for both metric and imperial users.
Calorie Calculator
Daily calorie needs based on age, sex, weight, height, and activity level using the Mifflin-St Jeor equation.
Tip Calculator
Calculate tip and split the bill across any group size. Handles tax-inclusive and tax-exclusive subtotals.
Loan Calculator
Monthly payment and total interest for a fixed-rate loan. Includes a simple amortisation table.
Salary Calculator
Gross-to-net pay with the major Korean deductions (income tax, national pension, health insurance, employment insurance).
Tax Calculator
Income-tax estimation by bracket. Brackets are documented in the guide and updated when tax law changes.
Currency Converter
Live FX-rate conversion across major currencies for travel, online shopping, and remittance estimates.
Our Principles
Free Forever
No paywalls, no premium tier. Ads keep tools free for everyone.
Privacy-First
All processing happens in your browser. Your data never leaves your device.
Fast by Default
Sub-second load times powered by Cloudflare's global edge network.
Open Access
No login, no signup, no email required. Just open and use.
Mobile-First
Every tool is touch-friendly and works great on phones and tablets.
No Dark Patterns
No fake countdown timers, no roach-motel cookie banners, no manufactured scarcity.
Technology Stack
We chose every piece of the stack to optimise for read speed, write speed, and long-term maintainability with a small team.
Our frontend is built on SvelteKit and TypeScript, styled with Tailwind CSS, and deployed to Cloudflare Pages. We use no traditional backend: pages are statically pre-rendered or generated at request time at the edge, calculator/tool logic runs entirely in the user's browser, and dynamic features that need persistence use the user's own localStorage.
This architecture has practical consequences for you. First, time-to-interactive is measured in tens of milliseconds, not seconds. Second, your inputs never leave your device, so there is no server log to leak. Third, our infrastructure cost is low enough that we can keep SD.gy free indefinitely without ever introducing a "Pro" tier.
Privacy Promise
All everyday calculators on SD.gy run client-side in your browser. The text, files, or values you input are never transmitted to our servers. The only data we collect is standard, aggregated analytics (page views, country, device type) and AdSense-related cookies as described in our Privacy Policy. We never sell or share personal data, we never read your inputs, and we never use your activity to train machine-learning models.
If our ad provider changes its consent rules, we will update the consent banner immediately and post a clear changelog entry on the Privacy Policy page. We treat consent as a permanent design choice, not a compliance afterthought.
Contact Us
Have questions, suggestions, or feedback? We'd love to hear from you.
- General questions and feedback: contact@sd.gy
- Bug reports: please include reproduction steps, browser, and OS.
- Tool suggestions: tell us which calculation or utility you wish existed — real use-cases move our roadmap.
- Partnership and content collaboration: include "Partnership" in your subject line.
- Press and media: same e-mail address, with "Press" in the subject line.
Legal & Operator Information
SD.gy is operated by SDK Co., Ltd., a Korean corporation registered with the Republic of Korea's Ministry of the Interior and Safety and the Korean Fair Trade Commission.