A

Author

Alex Doyle

Personal Finance & Technology Writer · calculatorapp.io

44
Guides
9
Categories
2024
Writing since

About Alex

Alex Doyle is a personal finance and technology writer at calculatorapp.io. He specializes in turning complicated math into plain-English explanations — the kind that actually help you make a decision, not just understand a concept in the abstract.

His work spans personal finance (mortgages, compound interest, 1099 vs W2 tax math, VA disability ratings, retirement projections), health and nutrition science (TDEE, BMR, calorie deficits, protein targets, pregnancy timelines), and AI cost analysis (API pricing, subscription ROI, LLM margin math). The common thread: every article is built around a calculator, and every calculator is built around a real question people are trying to answer.

Before joining calculatorapp.io, Alex spent several years in data journalism and financial content, where he developed an obsession with the gap between how financial math is taught and how people actually use it day-to-day. He holds a background in economics and has spent time in both editorial and product roles at digital finance publications.

His approach: skip the preamble, show the formula, give a real worked example, then let the calculator handle the rest.

Areas of Expertise

Personal Finance & Mortgages
Tax Planning (1099, W2, Brackets)
Health & Nutrition Math
AI Tools & Cost Analysis
Compound Interest & Investing
Retirement & Savings Planning
Calorie Science & TDEE
Lifestyle & Utility Calculators
Fact-check policy: All financial formulas and health equations are sourced from IRS publications, CDC/WHO guidelines, and peer-reviewed literature. Calculator methodology is documented on each tool page.

Articles by Alex Doyle

Financial
How to Calculate Your Monthly Mortgage Payment
P&I formula, PITI breakdown, PMI threshold, and 15 vs 30-year comparison with real numbers.
Financial
Compound Interest Explained: Formula, Examples & APY vs APR
Why $10,000 invested at 7% becomes $76,000 in 30 years — and the exact math behind it.
Financial
Compound Interest Guide: The Complete 2026 Breakdown
Daily vs monthly compounding, contribution frequency effects, and a full worked example from $0 to $1M.
Financial
House Hacking: How to Live for Free (or Close to It)
How house hacking works, real cash flow scenarios, and the mortgage offset math behind every strategy.
Financial
Rental Property Cash Flow: How to Calculate It
NOI, cap rate, cash-on-cash return, and GRM — the four numbers every rental investor needs.
Financial
Rental Cash Flow Guide: Real Numbers from Real Properties
What good cash flow actually looks like in 2026 — with worked examples across three property types.
Financial
Personal Loan vs Credit Card: Which Costs Less?
The real interest math, when a balance transfer wins, and the break-even calculation for debt consolidation.
Financial
VA Disability Combined Rating: How the Whole-Person Method Works
Step-by-step walkthrough of the VA's combined rating formula — and why 50% + 50% doesn't equal 100%.
Income
1099 vs W2: The Real Tax Difference & True Take-Home Pay
Self-employment tax, the QBI deduction, and what contractors actually need to charge to break even with salaried employees.
Income
1099 vs W2: True Cost Comparison
Benefits gap, retirement contributions, health insurance — the full picture beyond just SE tax.
Health
BMI Guide: What Your Number Means & Where the Formula Breaks Down
WHO/CDC categories, healthy weight ranges by height, and why BMI systematically misleads athletes.
Health
What Is BMI? The Formula, the History, and the Limits
Where BMI came from, how it's calculated, and what it can't tell you about your health.
Health
How Many Calories Should I Eat Per Day? Calculate Your TDEE
Why the FDA's 2,000-calorie baseline is probably wrong for you — and how to calculate your actual number.
Health
How Many Calories Per Day? The Mifflin-St Jeor Method
BMR, TDEE, and activity multipliers — the most accurate equation for estimating daily calorie needs.
Health
How Much Protein Per Day? Science-Backed Targets for Every Goal
Why the RDA of 0.8g/kg is the minimum to prevent deficiency — not the optimal amount for active people.
Health & Lifestyle
Calorie Deficit for Weight Loss: How Big Should It Be?
Safe deficit ranges, why too large a deficit backfires, and how to calculate the right target for your pace.
Health & Lifestyle
Calorie Deficit for Weight Loss: The Complete Science
3,500 calories per pound is a myth — here's the more accurate model and what it means for your weekly target.
Health
Baby Size by Week: Complete Pregnancy Guide (Weeks 4–40)
Size comparisons, weight, symptoms, milestones, and due date calculation across all 40 weeks.
Lifestyle
Sleep Timer: What It Is, How It Works & Why You Should Use One
90-minute sleep cycles explained, and how to find the bedtime that means you wake up between cycles instead of mid-dream.
Lifestyle
Intermittent Fasting Guide: Which Protocol Actually Works for You
16:8, 18:6, OMAD, 5:2, and alternate-day fasting compared side by side — with the research behind each.
Lifestyle
Steps to Calories: How Many Calories Does Walking Actually Burn?
The MET-based formula, how weight and pace affect the math, and why 10,000 steps is an arbitrary target.
Lifestyle & Finance
Fuel Cost Guide 2026: Gas Prices, Road Trip Costs & EV Comparison
How to calculate fuel cost for any trip, what's driving gas prices in 2026, and a real EV vs gas cost breakdown.
AI Tools
Is ChatGPT Plus Worth It in 2026? An Honest $20/Month Breakdown
Break-even math at every hourly rate, a full Free vs Plus feature comparison, and the $0.91/workday analysis.
AI Tools
AI API Cost Guide: Claude vs GPT vs Gemini Pricing Explained
Input/output token pricing, context window costs, and which model is cheapest for which workload in 2026.
AI Tools
AI API Cost Comparison 2026: Every Major Model Priced Out
Claude, GPT-5.4, Gemini 3.1 — cost per 1M tokens, cost per query, and cost at scale for real workloads.
AI Tools
AI ROI: What LLMs Actually Return — and Which Jobs Are Really at Risk
Real ROI math (757% year-1 worked example), automation displacement data, and hidden implementation costs.
AI Tools
Anthropic IPO Valuation: Timeline, Funding History & What It Would Mean
Anthropic's private valuation sits between $18B and $61B. Here's what an IPO would look like and what would trigger it.
Cooking
Coffee to Water Ratio Guide: The Perfect Ratio for Every Brew Method
SCA Golden Ratio, French press 1:15, espresso 1:2, cold brew 1:4 — every method's correct ratio, explained.
Cooking
Food Cost Per Serving: How to Calculate It
The exact formula to calculate food cost per serving, and how restaurants use food cost percentage to price their menus.
Cooking
How Much Food Per Person? The Real Numbers for Parties & Meal Prep
Catering-standard quantities for dinner parties, buffets, holidays, and meal prep — per person, per protein type.
Cooking
Baking Pan Size Guide: Volume Ratios & Substitution Math
9×13 to bundt, round to square — the volume math for swapping pan sizes without ruining your bake.
Cooking
How to Scale a Recipe: The Math Behind Doubling & Halving
Scaling factor, which ingredients don't scale linearly, and the leavening trap that ruins doubled cakes.
Math & Utility
Metric to Imperial Guide: Every Conversion You Actually Need
cm to inches, kg to lbs, Celsius to Fahrenheit — the complete reference table plus the formulas behind each.
Math & Utility
What Is a Good Tip Percentage? The Complete 2026 Tipping Guide
Standard percentages by service type, why 20% became the new baseline, and how to handle tip creep.
Math & Utility
Probability Calculator Guide: Single Events, Combined, & Conditional
P(A), P(A and B), P(A or B), and Bayes' theorem — the four types of probability questions with worked examples.
Math & Utility
GPA Calculator Guide: How to Calculate GPA & Whether It Actually Matters
4.0 scale, weighted GPA, cumulative vs semester — plus an honest look at what admissions offices actually care about.
Math & Utility
Free Online Calculators: The Complete Guide
Every calculator on calculatorapp.io explained — what it does, when to use it, and what to do with the result.
Tools
Free Online Tools Guide: QR Codes, Barcodes, Color Pickers & More
Every browser-based tool on the site — what each does, who it's for, and when you'd actually reach for it.
Tools
Free QR Code Generator Guide: Every Type & Use Case
URL, WiFi, vCard, PDF — static vs dynamic, how to add a logo, PNG vs SVG, and when to use each type.
Tools
Barcode Generator Guide: Code 128, EAN-13, UPC & More
When to use each barcode type, how to generate them free, and what Amazon FBA actually requires.
Tools
DOCX to PDF: How to Convert Without Uploading Your File
Browser-local conversion — no server, no account, no data leaving your device. Here's how it works.
Tools
Catan Board Generator: Balanced Randomization Explained
How the balanced mode prevents 6 and 8 tokens from sitting adjacent — and why it matters for game fairness.
Tools
Spin the Wheel: Random Decision Making That's Actually Fair
How cryptographic randomness works in a browser-based wheel — and why it beats drawing from a hat.
Tools
Random Generator Tools: The Ultimate Guide to Pickers & Randomizers
Name pickers, decision wheels, giveaway randomizers, team generators — what each does and when to use it.