When Is Refinancing Your Mortgage Worth It?
Refinancing pays off when monthly savings cover the closing costs before you move or sell. See the break-even math, the rate-drop rule of thumb, and what to check.
Camille Laurent · 3 min read
Guides & tutorials
Practical guides, how-tos and comparisons to get the most out of our free online tools.
March 3, 2026
March 2, 2026
Tongue Weight Is the Number That Stops a Trailer Swaying
Towing limits tell you whether you may hitch up. Tongue weight tells you whether the combination will stay straight. It is set by where the trailer's centre of gravity sits relative to its axle, it moves faster than anyone expects, and the recommended bands are not the same on the two sides of the Atlantic.
Marco Bianchi · 13 min read
Where the Weight Sits Decides How the Car Behaves
Two axle weights and a wheelbase give you the exact position of a car's centre of gravity. From there the arithmetic keeps going: how much weight braking moves forward, why the rear axle is the one that runs out of grip, and why a load behind the rear axle takes weight off the front.
Marco Bianchi · 13 min read
How to Train With Percentages of Your 1RM
Percentage-based training scales every lift to your one-rep max. Learn the strength and hypertrophy zones and how to set your working weights.
Aisha Karim · 4 min read
How a 401(k) Employer Match Works (Free Money)
An employer 401(k) match is free money: your company adds to your retirement savings when you contribute. See common match formulas, vesting, and why to grab the full match.
Camille Laurent · 3 min read
February 27, 2026
Startup Burn Rate and Runway: How Long Your Cash Lasts
Burn rate is how fast a startup spends cash each month. Learn to compute net burn, turn it into runway with cash ÷ burn, and read the number before it reads you.
Daniel Okonkwo · 4 min read
How to Find Your Target Weight for a Healthy BMI
The healthy BMI band of 18.5–24.9 turns into a weight range once you know your height. Here is how to work out yours step by step.
Sofia Nunes · 3 min read
What Would You Weigh on Other Planets?
Weight depends on gravity, but mass does not — here is why you would weigh differently on the Moon, Mars and Jupiter, and how to work it out.
Sofia Nunes · 2 min read
February 26, 2026
How to Calculate a Grade Average: Weighted Grades and GPA
A grade average is the weighted mean of your grades: each grade times its weight, summed, divided by the total weight. Learn the method, a worked example, and how GPA differs from a percentage.
Lena Hoffmann · 5 min read
How Much Does an Appliance Cost to Run? A Simple Method
Turn an appliance's wattage and daily hours into an annual running cost using one formula: power times hours times your price per kWh.
Marco Bianchi · 3 min read
How Fast Do Cars Depreciate? The Value Curve
New cars lose value fastest in year one, then 15–20% a year. See the depreciation curve, why the first year hits hardest, and a worked example.
Camille Laurent · 3 min read
February 25, 2026
Blood Donation Intervals, and What Your Body Is Actually Replacing
Plasma is back in a day, red cells in weeks, iron in months — and it is the iron that sets the interval. The arithmetic of a unit, and the minimum intervals published by seven national services.
Sofia Nunes · 14 min read