Are these calculators accurate enough for real decisions?

The math itself is exact (e.g. BMI = kg / m², Naegele's rule for due dates). They are general-purpose estimates, not professional advice — for medical or legal decisions, consult a qualified professional.

Do you store the values I type in?

No. Inputs live only in your browser tab and are wiped the moment you close it. There is no analytics call carrying your numbers.

Why does the BMI calculator support both metric and imperial?

Because health charts use both. We let you pick units rather than forcing a conversion that introduces rounding errors.

Can I use these calculators offline?

After the first load, yes — they don't need a network round-trip to compute a result.

Free Online Calculators

Quick, accurate, ad-free everyday calculators.

Your files never leave your device. No upload. No sign-up.

From splitting a restaurant bill to figuring out exactly how far along a pregnancy is, SwiftTooly's calculators give you a clear answer in a single screen. They run on the math built into your browser — no servers, no accounts, no analytics on the numbers you type. Bookmark any one of them and you have an instant answer next time you need it.

8 calculators

Age Calculator

Calculate your exact age in years, months, and days.

Percentage Calculator

Calculate percentages, ratios, and percentage change.

Tip Calculator

Quickly calculate the tip and split a bill between any number of people.

Discount Calculator

Find the sale price and the amount saved for any percentage discount.

BMI Calculator

Calculate Body Mass Index in metric or imperial units, with a category result.

Pregnancy Due Date Calculator

Estimate your due date, current week, and trimester from your last period.

Time Duration Calculator

Calculate the duration between two times, including overnight shifts.

Unit Converter

Convert length, weight, temperature, volume, speed and more.

Why use SwiftTooly's calculators

Honest math

Documented formulas, no surprise add-ons, no marketing layer on top of the result.

Private inputs

Your weight, age, due date and tip amount stay on your device — we never see them.

Mobile-first

Large tap targets and number inputs make these usable one-handed on a phone.

Zero ads in the way

A clean interface focused on the answer, not on keeping you on the page.

Browser-based vs upload-to-server

SwiftTooly (browser)

Every formula runs in a few lines of JavaScript inside the tab. You can disable the network and the calculator still works.

Typical upload-to-server tools

Many sites round-trip even simple math to a backend so they can log inputs, A/B test, or attach them to your profile.

Related collections

Unit conversion pages

Pre-set converters for km↔miles, kg↔lbs, °C↔°F, cups↔ml, mph↔km/h and more — each with formula and quick reference.

Frequently asked questions

Are these calculators accurate enough for real decisions?: The math itself is exact (e.g. BMI = kg / m², Naegele's rule for due dates). They are general-purpose estimates, not professional advice — for medical or legal decisions, consult a qualified professional.
Do you store the values I type in?: No. Inputs live only in your browser tab and are wiped the moment you close it. There is no analytics call carrying your numbers.
Why does the BMI calculator support both metric and imperial?: Because health charts use both. We let you pick units rather than forcing a conversion that introduces rounding errors.
Can I use these calculators offline?: After the first load, yes — they don't need a network round-trip to compute a result.