How Much Emergency Fund Do I Need?
How to choose an emergency fund target based on essential costs, income stability and realistic monthly saving.
Guides
Guides for better calculations
Read the notes behind the numbers, from mortgage payments and calorie targets to CPC, shoe sizing and material estimates.
Guide topics
Browse by calculation area
Each topic gathers the calculators, articles and assumptions that belong together.
16 guidesFinanceSalary, mortgage, loan, savings and budgeting guides for decisions where the assumptions matter.6 guidesHealthHealth and fitness guides with careful limits around estimates, trends and screening measures.5 guidesMathsCommon maths guides for checking formulas, avoiding mistakes and understanding the working.3 guidesScienceScience and engineering guides for formulas where measurement details change the answer.4 guidesSizesSizing guides for clothing, shoes and fit decisions where brand charts and measurements matter.4 guidesHomeRoom measurement and material guides for planning projects before ordering supplies.1 guideTimeDate, time and deadline guides for planning work, events and cut-offs without spreadsheet setup.11 guidesBusinessMarketing, pricing and business metric guides for turning calculator results into better decisions.
Featured reading
Good places to start
A few useful reads before you compare scenarios, change a budget or judge a result.
How Much Rent Can I Afford?
A practical way to compare rent, bills, income, debt payments and the money left for savings and everyday life.
Mortgage Affordability Checks Before You View Homes
How to estimate a property budget before viewings by combining income, deposit, debts, payment stress testing and monthly costs.
How to Calculate Conversion Rate
A clear guide to conversion rate formulas for websites, retail, sales teams and marketing campaigns.
How to Calculate CPC
The cost per click formula, examples, and how to read CPC with CTR, conversion rate and cost per conversion.
Cost Per Conversion Formula
How to calculate cost per conversion, CPA and break-even acquisition cost from campaign spend and conversions.
All guide sections
Browse the library by topic
Each row shows the first six articles. Open the topic page for the full set.
Finance Calculator Guides
16 guides
Salary, mortgage, loan, savings and budgeting guides for decisions where the assumptions matter.
How to Calculate Mortgage Payments
A clear guide to monthly mortgage payments, interest, term length and loan-to-value.
Mortgage Overpayments vs a Shorter Term
How to compare monthly overpayments, term changes and interest saved on a repayment mortgage.
UK Take Home Pay Calculator Assumptions
Understand what a take-home pay calculator includes, what it leaves out and why payroll can differ.
APR vs Interest Rate: What Changes the Real Cost?
A clear guide to APR, interest rates, fees and the real cost of borrowing.
How to Build a Monthly Budget That Still Works in Real Life
A practical guide to splitting income between bills, spending, debt, savings and annual costs.
How Inflation Changes Savings Goals
Why a future target may need to be higher than today's price, and how to plan for it.
Health and Fitness Calculator Guides
6 guides
Health and fitness guides with careful limits around estimates, trends and screening measures.
Using Calories and Macros as a Starting Point
How to interpret calorie and macro estimates without treating them as exact prescriptions.
BMR, TDEE and Calories: What Is the Difference?
Understand basal metabolic rate, activity estimates and how they become a daily calorie target.
Heart Rate Zones for Running, Cycling and Fitness
How to use heart rate zones for easy training, threshold work and recovery without over-reading the numbers.
BMI, Body Fat and Waist-to-Hip Ratio Compared
What common body measurement calculators can and cannot tell you about health context.
Calorie Deficit, Maintenance and Surplus: How to Choose
How to move from estimated maintenance calories to a fat loss, maintenance or muscle gain target.
Running Pace vs Speed: What to Use in Training
How pace, speed, distance and heart rate zones work together for runners and cyclists.
Maths Calculator Guides
5 guides
Common maths guides for checking formulas, avoiding mistakes and understanding the working.
Percentage Change: Common Mistakes and Quick Checks
How to avoid common percentage errors in discounts, increases, comparisons and ratios.
Standard Deviation and Probability in Plain English
A practical explanation of spread, variation and probability for everyday data checks.
Area and Volume Calculations for Materials
How to move from measurements to paint, tiles, concrete and other material estimates.
Fractions, Ratios and Percentages: How They Connect
A practical guide to moving between fractions, ratios and percentages without losing the base value.
GPA, Credits and Weighted Averages
How GPA uses credits, why weighted averages matter and where school policies can change the result.
Science and Engineering Calculator Guides
3 guides
Science and engineering guides for formulas where measurement details change the answer.
Density, Force and Pressure: Units That Need Care
A guide to common science and engineering calculations where units make or break the result.
Concentration, Dilution and pH Calculations
How to think about molarity, dilution and pH when checking chemistry calculations.
Common Unit Conversion Mistakes and How to Avoid Them
How to avoid errors with length, weight, temperature, volume, density and pressure conversions.
Fashion and Size Calculator Guides
4 guides
Sizing guides for clothing, shoes and fit decisions where brand charts and measurements matter.
How Shoe Size Conversion Works
A practical guide to comparing UK, US, EU and Mondopoint shoe sizes, with fit checks and measurement tips.
Kids Shoe Size by Foot Length
How to measure a child's foot length, allow growth room and use UK or EU shoe size estimates safely.
How to Measure Yourself for Clothing Sizes
A practical measuring guide for dress sizes, jeans, bras and international clothing conversions.
Dress Size Conversion and Brand Fit Guide
How to compare dress sizes across countries and brands without relying on the label alone.
Home and DIY Calculator Guides
4 guides
Room measurement and material guides for planning projects before ordering supplies.
How to Measure a Room for DIY Materials
A room-by-room guide to estimating paint, tiles, concrete, heating needs and moving boxes.
Tile Waste, Layout and Ordering Guide
How to estimate tiles for a room, choose a waste allowance and avoid ordering too little.
How to Measure for Wallpaper Rolls
How to measure walls, account for openings, choose a waste allowance and avoid running short on wallpaper.
Flooring Packs, Waste and Room Measurements
How to estimate flooring packs for laminate, vinyl or engineered wood without under-ordering materials.
Time and Date Calculator Guides
1 guide
Date, time and deadline guides for planning work, events and cut-offs without spreadsheet setup.
Working Days, Hours and Deadline Planning
How to calculate business days, elapsed hours, date gaps and countdowns without losing track of weekends.
Business and Marketing Calculator Guides
11 guides
Marketing, pricing and business metric guides for turning calculator results into better decisions.
How to Calculate Conversion Rate
A clear guide to conversion rate formulas for websites, retail, sales teams and marketing campaigns.
How to Calculate CPC
The cost per click formula, examples, and how to read CPC with CTR, conversion rate and cost per conversion.
How to Calculate CPM
The CPM formula for paid media, with examples for impressions, campaign cost, CPC, CTR and cost per conversion.
Cost Per Conversion Formula
How to calculate cost per conversion, CPA and break-even acquisition cost from campaign spend and conversions.
Website, Sales and Retail Conversion Rates
How to choose the right conversion rate formula for ecommerce, lead generation, sales teams and retail stores.
CPC, CPM, Conversion Rate and ROI Explained
A marketer's guide to the core metrics behind paid campaigns and performance reporting.