EvvyTools Blog
Smart guides, how-tos, and tool deep dives. Better decisions start with better understanding.
Health & Wellness
How Much Caffeine Is Safe Per Day Based on Body Weight
A flat 400mg caffeine guideline ignores body weight and individual tolerance. Calculating your limit based on weight and beverage half-life produces a more useful daily target.
Financial Literacy
How Extra Mortgage Payments Shorten Your Loan and Reduce Total Interest
Extra mortgage payments cut years off your loan and save thousands in interest. Here is the math and the strategy behind principal-first paydown.
Financial Literacy
How to Calculate Lumber Quantities for Any Woodworking Project
Getting lumber quantities wrong wastes money and trips. Here's how to calculate board feet and build accurate material lists for any woodworking project.
Health & Wellness
Riegel's Formula Explained: How Race Time Prediction Actually Works
Peter Riegel's power law formula predicts race times across distances using a fatigue exponent of 1.06. Here is how it works, what drives the math, and when to trust it.
Health & Wellness
How to Run Negative Splits: The Pacing Strategy Behind Faster Race Times
A negative split means finishing the second half of a race faster than the first. Here is the physiology, the math, and the race-day execution strategy every runner needs.
Tool Deep Dives
How Password Entropy Works and Why It Matters for Account Security
Password entropy quantifies how unpredictable a password is. Understanding the formula helps you build credentials that hold up against real attacks.
Financial Literacy
How to Calculate ROAS and Make Your Ad Spend Actually Profitable
Learn how to calculate Return on Ad Spend, understand break-even ROAS, and use the numbers to identify which ad campaigns are actually worth keeping.
Tool Deep Dives
How DNS Lookups Diagnose Email Deliverability Issues
Use DNS lookups to inspect MX, SPF, DKIM, and DMARC records before sending email, and catch the configuration problems that trigger spam filters.
How-To Guides
Tree Age Estimation: How Trunk Diameter Reveals a Tree's History
Most trees don't come with birth certificates. Here's how to estimate age from trunk size using the same method professional arborists use.
Financial Literacy
How the 28/36 Rule Determines How Much House You Can Actually Afford
Run the 28/36 numbers before you fall for a listing. Here is what each ratio measures and how to set a home budget that actually holds up.
Financial Literacy
How the 50/30/20 Budget Rule Works (And Where It Falls Short)
The 50/30/20 rule is simple in theory. In practice, rent alone can blow past half your paycheck. Here's an honest look at each bucket.
Tool Deep Dives
JWT Token Structure: How to Decode and Read Authentication Tokens
JSON Web Tokens look like gibberish but contain readable authentication data. Here is how to decode and understand every part.