📘 Toolfyra Book Guides
Long-form handbooks, one chapter at a time — written to be read, not skimmed.
📘 Airbnb Profit Calculator · COMPLETE HANDBOOK
Airbnb Profit: The 2026 Guide to Short-Term Rental Math
How to estimate short-term rental profit honestly: revenue from nightly rate and occupancy
📘 Boat Loan Calculator · COMPLETE HANDBOOK
Boat Loans in 2026: Rates, Terms, and the 15-Year Ceiling
A complete 2026 guide to boat financing: typical rates, terms up to 15 years, survey and i
📘 BSA Calculator · COMPLETE HANDBOOK
Body Surface Area (BSA): The 2026 Guide to Du Bois, Mosteller, and Why Medicine Uses It
A clear 2026 guide to body surface area: the Du Bois and Mosteller formulas, where BSA is
📘 CAC Calculator · COMPLETE HANDBOOK
CAC: The 2026 Guide to Customer Acquisition Cost
What CAC measures, what belongs in the numerator, paid versus blended views, payback perio
📘 Capital Gains Tax Calculator · COMPLETE HANDBOOK
Capital Gains Tax Calculator: The Complete 2026 Guide
How capital gains tax actually works in 2025-2026: brackets, holding periods, NIIT, and th
📘 Car Accident Settlement Calculator · COMPLETE HANDBOOK
Car Accident Settlement Calculator Guide 2026: How the Multiplier Method Really Works
How a car accident settlement calculator estimates value with the multiplier method, the r
📘 Car Insurance Estimator · COMPLETE HANDBOOK
Car Insurance Estimates in 2026: What an Estimator Can and Cannot Tell You
How car insurance estimators work: the rating factors that move rates, coverage structure,
📘 Conduit Fill Calculator · COMPLETE HANDBOOK
Conduit Fill: The 2026 Guide to NEC Fill Rules and Conductor Counts
How NEC conduit fill works: the 53, 31, 40, and 60 percent rules, Chapter 9 Tables 4 and 5
📘 Customer Lifetime Value Calculator · COMPLETE HANDBOOK
Customer Lifetime Value: The 2026 Guide to Estimating CLV
How to estimate customer lifetime value honestly: the historic formula, the churn-based fo
📘 Debt Avalanche Calculator · COMPLETE HANDBOOK
The Debt Avalanche: A 2026 Guide to Paying Off Debt by Interest Rate
How the debt avalanche works: rank debts by APR, pay minimums plus one concentrated extra,
📘 Disability Insurance Calculator · COMPLETE HANDBOOK
Disability Insurance Calculator Guide 2026: Sizing Income Protection
A 2026 guide to disability insurance math: replacing 60 percent of income, taxable vs tax-
📘 Escrow Calculator · COMPLETE HANDBOOK
Escrow Accounts Explained: The 2026 Guide to Your Mortgage's Quiet Third Line
How mortgage escrow works in 2026: PITI, the RESPA two-month cushion, shortage and surplus
📘 Estate Tax Calculator · COMPLETE HANDBOOK
Estate Tax Calculator: The Complete 2026 Guide
How the federal estate tax works for 2025-2026: the 13.99-million-dollar exemption, the 40
📘 EV Charging Cost Calculator · COMPLETE HANDBOOK
EV Charging Cost Guide 2026: Rates, Efficiency, and Cost per Mile
A 2026 guide to what charging an EV really costs: residential rates from about $0.10 to $0
📘 FERS Retirement Calculator · COMPLETE HANDBOOK
FERS Retirement Calculator Guide 2026: High-3, Multipliers, and MRA
A 2026 guide to the FERS basic annuity: the 1% and 1.1% multipliers, how high-3 salary wor
📘 Fertilizer Calculator · COMPLETE HANDBOOK
Lawn Fertilizer Math: The 2026 Guide to Bag Ratios, Target Rates, and How Much to Apply
How fertilizer math works: reading N-P-K on the bag, the half-pound to one-pound nitrogen
📘 FSA Calculator · COMPLETE HANDBOOK
FSA Calculator Guide 2026: Plan Your Flexible Spending Account
A practical 2026 guide to flexible spending accounts: the roughly $3,300 health FSA limit,
📘 GFR Calculator (CKD-EPI 2021) · COMPLETE HANDBOOK
eGFR and the GFR Calculator: The 2026 Guide to Reading Your Kidney Numbers
A plain-English 2026 guide to eGFR: the CKD-EPI 2021 race-free equation, the G1 to G5 stag
📘 Gift Tax Calculator · COMPLETE HANDBOOK
Gift Tax Calculator: The Complete 2026 Guide
How the gift tax works for 2025-2026: the 19,000-dollar annual exclusion, the 38,000 split
📘 Gravel Driveway Calculator · COMPLETE HANDBOOK
Gravel Driveway Math: The 2026 Guide to Cubic Yards, Tonnage, and Ordering the Right Amount
How gravel driveway math works: converting depth to cubic yards, the roughly 1.4 tons per
📘 Grout Calculator · COMPLETE HANDBOOK
Grout Math: The 2026 Guide to Coverage, Bags, and the Formula Factors
How a grout calculator works: the coverage formula and its factors — tile size, joint widt
📘 Hourly to Salary Calculator · COMPLETE HANDBOOK
Hourly to Salary: The 2026 Guide to Annualizing a Wage Without Fooling Yourself
A clear 2026 guide to converting hourly pay to annual salary: the 2,080-hour baseline, the
📘 HVAC Load Calculator · COMPLETE HANDBOOK
HVAC Load Sizing: The 2026 Guide to BTU Estimates, Zone Factors, and Right-Sizing Your System
How HVAC load sizing works: simplified BTU-per-square-foot estimates by climate, the facto
📘 Ideal Body Weight Calculator · COMPLETE HANDBOOK
Ideal Body Weight in 2026: The Devine Formula, BMI Bands, and What 'Ideal' Actually Means
A clear 2026 guide to ideal body weight: the Devine formula step by step, how BMI bands re
📘 Insurance Premium Calculator · COMPLETE HANDBOOK
Insurance Premium Calculator Guide 2026: How Insurers Build Your Price
A 2026 guide to how insurance premiums are built: base rates, per-$1,000 pricing, age and
📘 Interest Only Mortgage Calculator · COMPLETE HANDBOOK
Interest-Only Mortgages in 2026: A Complete Borrower's Guide
How interest-only mortgages work in 2026: typical rates and structures, who benefits, how
📘 Land Loan Calculator · COMPLETE HANDBOOK
Land Loans in 2026: Rates, Down Payments, and Terms Explained
A complete 2026 guide to financing land: raw versus improved parcels, typical rates and do
📘 Life Insurance Needs Calculator · COMPLETE HANDBOOK
Life Insurance Needs Calculator Guide 2026: The DIME Method and Beyond
A 2026 guide to sizing life insurance: the DIME method, income replacement ratios, what to
📘 Loan Payoff + Extra Payments · COMPLETE HANDBOOK
Extra Payments and Loan Payoff: The 2026 Guide to Amortization, Interest Savings, and Faster Freedom
How loan payoff math works: amortization schedules, why early payments are mostly interest
📘 Margin Loan Calculator · COMPLETE HANDBOOK
Margin Loans Explained: The 2026 Guide to Borrowing Against Your Portfolio
How margin loans work in 2026: initial and maintenance margin, daily interest on the debit
📘 Mortgage Points Calculator · COMPLETE HANDBOOK
Mortgage Points in 2026: When Buying Down Your Rate Pays Off
A plain-English 2026 guide to mortgage discount points: what a point costs, how much rate
📘 Motorcycle Loan Calculator · COMPLETE HANDBOOK
Motorcycle Loans in 2026: Rates, Terms, and Smart Structure
A complete 2026 guide to motorcycle financing: typical rates of 7-14 percent, terms from 2
📘 Personal Injury Settlement Calculator · COMPLETE HANDBOOK
Personal Injury Settlement Calculator Guide 2026: The Method, the Ranges, the Reality
How personal injury settlement calculators work: the multiplier method explained, realisti
📘 Personal Loan Payment Calculator · COMPLETE HANDBOOK
Personal Loan Payments Explained: Amortization, Fees, and the APR Effect in 2026
How personal loan payments work: the amortization mechanics, how origination fees change t
📘 PMI Removal Calculator · COMPLETE HANDBOOK
PMI Removal Calculator Guide 2026: The 80 Percent and 78 Percent Rules Explained
A 2026 guide to removing private mortgage insurance: the 80% request rule, the 78% automat
📘 Property Tax Estimator · COMPLETE HANDBOOK
Property Tax Estimator Guide 2026: The Formula, the State Spread, and What Assessors Actually Do
How a property tax estimator works: market value to assessed value to millage, realistic e
📘 PTO Payout Calculator · COMPLETE HANDBOOK
PTO Payout in 2026: How the Math Works, How It's Taxed, and Where State Rules Change Everything
A complete guide to paid time off payouts: the rate-times-hours math, supplemental withhol
📘 Quarterly Estimated Tax Calculator · COMPLETE HANDBOOK
Quarterly Estimated Tax Calculator: The Complete 2026 Guide
Quarterly estimated taxes explained for 2026: who must pay, the 90/100/110 percent safe ha
📘 Rental Property ROI Calculator · COMPLETE HANDBOOK
Rental Property Returns: The 2026 Guide to NOI, Cap Rate, Cash-on-Cash, and the 1% Rule
How rental property ROI works: building net operating income, cap rate versus cash-on-cash
📘 ROAS Calculator · COMPLETE HANDBOOK
ROAS: The 2026 Guide to Return on Ad Spend
What ROAS measures, how break-even ROAS works, which benchmarks are commonly cited, and ho
📘 RV Loan Calculator · COMPLETE HANDBOOK
RV Financing in 2026: Rates, Terms, and the 20-Year Question
A complete 2026 guide to RV loans: typical rates, terms up to 20 years, down payments, dep
📘 Self Employment Tax Calculator · COMPLETE HANDBOOK
Self-Employment Tax Calculator: The Complete 2026 Guide
How the 15.3 percent self-employment tax works for 2025-2026: the 92.35 percent factor, th
📘 Severance Pay Calculator · COMPLETE HANDBOOK
Severance Pay Calculator Guide 2026: Benchmarks, Benchmarks' Limits, and the Deal Around the Number
How a severance pay calculator works: the weeks-per-year benchmarks, who is actually legal
📘 Sod Calculator · COMPLETE HANDBOOK
Sod Math: The 2026 Guide to Measuring, Pallets, and Ordering
How to measure a lawn for sod, the roughly 500 square foot pallet norm, slab and roll coun
📘 Topsoil Calculator · COMPLETE HANDBOOK
Topsoil Math: The 2026 Guide to Cubic Yards, Depths, and Ordering
How to calculate topsoil: the square-feet-times-inches-over-324 formula, depth choices by
📘 Towing Capacity Calculator · COMPLETE HANDBOOK
Towing Capacity Guide 2026: GVWR, Payload, GCWR, and Tongue Weight
A plain-language guide to towing limits: what curb weight, GVWR, payload, GCWR, and tongue
📘 Travel Insurance Cost Calculator · COMPLETE HANDBOOK
What Travel Insurance Should Cost: The 2026 Guide to the 4–10% Rule and What Moves It
A practical 2026 guide to travel insurance costs: the rough 4–10% of trip cost ballpark, w
📘 TSP Retirement Calculator · COMPLETE HANDBOOK
TSP Retirement Calculator Guide 2026: Limits, Match, and Projections
A 2026 guide to modeling your Thrift Savings Plan: 2025 contribution limits and how limits
📘 Wire Size Calculator · COMPLETE HANDBOOK
Wire Size: The 2026 Guide to Ampacity, Voltage Drop, and Choosing Gauge
How wire size is chosen: copper ampacity from the 75°C column, the 240.4(D) small-conducto
📘 Wrongful Termination Settlement Calc · COMPLETE HANDBOOK
Wrongful Termination Settlement Calculator Guide 2026: Components, Ranges, Reality
How a wrongful termination settlement calculator works: back pay, front pay, and distress