ProsperMath guides
Understand the decision behind the number.
Worked examples, trade-offs and official sources—each connected to a calculator so you can test the assumptions yourself.
How Much Should I Invest Each Month?
Work backwards from your goal, timeframe and current savings to choose a realistic monthly investment amount.
Read guide →InvestingLump Sum or Monthly Investing: Which Approach Fits?
Compare investing available cash immediately with phasing it into the market over time, including risk and behavioural trade-offs.
Read guide →InvestingWhat Is the Cost of Waiting to Invest?
See why a five-year investing delay can change a long-term projection even when the monthly contribution stays the same.
Read guide →InvestingHow Much Can Investment Fees Cost Over Time?
Understand how a seemingly small annual fee compounds into a much larger difference over a long investment period.
Read guide →PropertyShould You Overpay the Mortgage or Invest?
Compare the guaranteed interest saving from a mortgage overpayment with uncertain investment growth and liquidity.
Read guide →DebtDebt Avalanche vs Snowball: Which Method Saves More?
Compare paying the highest-interest debt first with clearing the smallest balance first, including a worked example.
Read guide →DebtWhy Credit Card Minimum Payments Cost So Much
See how interest and a low monthly payment can extend credit-card debt, plus how to test a faster repayment amount.
Read guide →SavingsHow Much Emergency Fund Do I Need?
Choose an emergency-fund target using essential monthly costs, income stability, dependants and access to other support.
Read guide →United KingdomHow the UK ISA Allowance Works in 2026/27
Understand the £20,000 adult ISA allowance for 2026/27, the Lifetime ISA sub-limit and flexible-ISA replacement rules.
Read guide →United KingdomDividend Reinvestment in the UK: ISA vs Taxable Account
See how reinvesting dividends can compound and how UK dividend tax outside an ISA can create long-term drag.
Read guide →United StatesHow Much 401(k) Employer Match Are You Leaving Unclaimed in 2026?
Translate a 401(k) matching formula into dollars and compare it with the 2026 employee contribution limits.
Read guide →CanadaTFSA Contribution Room in 2026: Mistakes to Avoid
Understand the C$7,000 TFSA dollar limit for 2026, unused room, withdrawals and common overcontribution mistakes.
Read guide →IncomeHow Much Is Your Pay Rise Really Worth After Inflation?
Calculate what a salary increase adds per month and paycheck, then measure whether your pay rise actually beats inflation.
Read guide →SavingsHow Much Interest Will $10,000 Earn in a Year?
See how APY or AER, account requirements, tax and inflation change the interest earned on 10,000 in a savings account.
Read guide →SavingsAPY vs Interest Rate: What Actually Changes?
Understand how APY, AER, nominal interest rates and compounding frequency affect savings-account comparisons.
Read guide →InvestingWhat Is Your Investment Return After Fees and Inflation?
Convert a headline investment return into a more useful estimate after annual costs and the loss of purchasing power.
Read guide →PropertyWhat Does a 1% Mortgage Rate Rise Do to Your Payment?
See how mortgage balance, remaining term and repayment type determine the cost of an interest-rate increase.
Read guide →DebtHow Much Extra Should You Pay on a Credit Card?
Compare the payoff time and interest cost of different monthly payments before choosing an amount your budget can sustain.
Read guide →SavingsHow to Use Sinking Funds for Annual Bills and Irregular Expenses
Plan monthly savings for annual bills, repairs, holidays and other predictable costs without treating every bill like an emergency.
Read guide →BudgetingHow Much Are Subscriptions Really Costing You?
Add up streaming, app, membership and software subscriptions, then estimate their annual and multi-year cost.
Read guide →BudgetingHow to Calculate Your Net Worth Without Overcomplicating It
Use a simple assets-minus-debts approach to track financial progress, liquidity and debt exposure over time.
Read guide →BudgetingHow to Calculate Your Savings Rate
Work out the share of take-home income going toward cash savings, investments and extra debt repayment.
Read guide →PropertyCan You Overpay an Interest-Only Mortgage?
Learn how lump-sum and monthly capital overpayments can affect an interest-only mortgage balance, payment and term-end shortfall.
Read guide →PropertyMortgage Overpayment: Reduce the Term or Lower the Payment?
Compare what happens when a lump-sum mortgage overpayment shortens the term versus reducing the required monthly payment.
Read guide →UK property taxStamp Duty on a House in 2026: Bands, First-Time Buyers and Second Homes
Understand how Stamp Duty Land Tax is calculated in England and Northern Ireland, including first-time buyer relief and higher rates for additional properties.
Read guide →US retirementHow to Calculate Your RMD for 2026
Learn the standard RMD formula for 2026, the prior-year balance to use and when a different IRS life-expectancy table may apply.
Read guide →US incomeHow to Calculate Overtime Pay and Taxes
Calculate time-and-a-half overtime, understand why withholding can look high and estimate the amount left after simple payroll tax assumptions.
Read guide →MortgagesHow to Calculate Mortgage Payments
Understand the principal-and-interest mortgage payment formula, what determines the monthly payment and why taxes and insurance can make the real bill higher.
Read guide →How we publish
Examples you can reproduce.
Every guide identifies its assumptions, links to the calculator used for worked examples and cites official sources for regional limits. Guides are reviewed when rules change and clearly state their review date.