Financial calculators that use your country's actual rules

Divide the annual interest rate by 12 to get the monthly rate, then apply the amortisation formula: M = P × r(1+r)^n / ((1+r)^n − 1), where P is the principal, r the monthly rate, and n the number of monthly payments. For a $300,000 loan at 6% over 30 years, this gives $1,799 per month. Different countries use different compounding conventions: Canadian fixed-rate mortgages compound semi-annually, which changes the effective monthly rate.

A fixed-rate mortgage locks your interest rate for a set period - typically 2–30 years depending on the country - so your monthly payment stays the same. A variable rate moves with a reference rate such as the Bank of England base rate or US SOFR, so your payment can rise or fall. Fixed rates provide payment certainty; variable rates are often lower initially but carry repricing risk.

The minimum deposit depends on the country and lender. In the US, conventional loans typically require 3–20%, while FHA loans allow 3.5%. In the UK, lenders usually want at least 5–10%, and Ireland's Central Bank caps most loans at 90% of the purchase price for first-time buyers. A larger deposit reduces the loan-to-value ratio and usually results in a lower interest rate.

Loan-to-value is the mortgage amount as a percentage of the property's purchase price or appraised value, whichever is lower. A $280,000 mortgage on a $350,000 home has an 80% LTV. Lenders use LTV to price risk: a lower LTV usually means a lower interest rate and no requirement for mortgage insurance (PMI in the US). Most countries have regulatory LTV caps for certain borrower types.

Remortgaging means replacing your current mortgage with a new one, either with your existing lender or a new one, usually to secure a lower interest rate or release equity. It makes financial sense when the monthly saving exceeds the combined exit fees, valuation, and legal costs within two to three years. In the UK, most borrowers remortgage when their fixed period ends to avoid reverting to the lender's standard variable rate.

The key financial comparison is the opportunity cost of the deposit and the monthly difference between owning costs (mortgage, maintenance, property tax) and rent. Buying is financially better when the price-to-rent ratio is low or when you plan to stay for many years. Renting preserves capital flexibility and avoids maintenance costs. The rent vs buy calculator computes the ten-year financial outcome of each option.

Personal loans use the standard amortisation formula: M = P × r(1+r)^n / ((1+r)^n − 1), where P is the loan amount, r is the monthly interest rate (annual rate ÷ 12), and n is the number of months. A $10,000 loan at 8% APR over 48 months gives a monthly payment of $244. Unlike mortgages, personal loans are unsecured and have no compounding convention differences across countries.

APR (Annual Percentage Rate) is the total cost of borrowing expressed as a yearly rate, including both the interest rate and mandatory fees such as origination fees. The interest rate only covers the cost of the money itself. If a lender charges 6% interest plus a 2% origination fee on a three-year loan, the APR is higher than 6% - often around 7.5–8% - because the fee is amortised over the loan term.

Auto loans are secured against the vehicle, which the lender can repossess if you default, while personal loans are typically unsecured. Because the lender holds collateral, auto loan rates are generally lower for the same borrower. Auto loans also factor in the vehicle purchase price, down payment, trade-in value, and in many US states, sales tax added to the financed amount.

Credit card minimum payments are typically set at 1–3% of the outstanding balance or a small fixed amount, whichever is greater. Paying only the minimum keeps the balance high for years because most of each payment covers interest, not principal. On a $5,000 balance at 20% APR with a 2% minimum payment, paying only the minimum takes over 30 years to clear and costs roughly $6,000 in interest - more than the original balance.

The debt snowball method pays off debts from smallest balance to largest, freeing up monthly cash flow quickly and providing psychological momentum. The debt avalanche pays from highest interest rate to lowest, minimising total interest paid over time. The avalanche saves more money mathematically, while the snowball may work better for people who need early visible progress to stay motivated.

The clearest comparison is total cost: multiply the monthly payment by the number of months and add any upfront fees for each loan. APR standardises this into a single annual rate, but total cost is more useful when terms differ significantly. A loan with a lower APR and a much longer term can cost more overall than one with a higher rate and shorter term.

Compound interest means you earn interest not just on your initial principal but also on previously accumulated interest. With annual compounding, $10,000 at 5% becomes $10,500 after one year and $11,025 after two years - the second year earns interest on $10,500, not just $10,000. More frequent compounding (monthly, daily) produces slightly higher returns. The formula is A = P(1 + r/n)^(nt), where P is principal, r the annual rate, n compounding periods per year, and t years.

Nominal return is the raw percentage gain on an investment. Real return adjusts for inflation, showing how much purchasing power actually increased. If a portfolio earns 7% in a year when inflation is 3%, the real return is approximately 4%. The precise calculation uses the Fisher equation: real return = (1 + nominal) / (1 + inflation) − 1. Real returns matter more for long-term planning because they reflect actual purchasing power, not just dollar amounts.

A common starting point is the 4% rule: multiply your expected annual spending in retirement by 25. To sustain $60,000 per year, you would need approximately $1,500,000. This assumes a diversified portfolio, a 30-year retirement horizon, and historical market returns. The right multiple depends on your planned retirement duration, risk tolerance, and whether you have other income sources such as a pension or social security.

The FIRE (Financial Independence, Retire Early) number is the portfolio size at which investment returns can sustain your spending indefinitely. It is calculated as annual expenses divided by your planned withdrawal rate - typically 4%, based on the Trinity Study. For $50,000 in annual spending at a 4% withdrawal rate, the FIRE number is $1,250,000. A lower withdrawal rate (such as 3%) produces a larger but safer target.

CAGR (Compound Annual Growth Rate) is the annualised rate at which an investment grew from its initial to its final value over a set period. The formula is CAGR = (Final Value / Initial Value)^(1 / years) − 1. If $10,000 grew to $17,000 over six years, the CAGR is approximately 9.2%. CAGR removes the effect of year-to-year volatility, making it useful for comparing investments of different sizes and durations on a like-for-like basis.

The duration depends on your portfolio value, annual withdrawal amount, investment return, and inflation rate. If your portfolio earns more than your inflation-adjusted withdrawal rate, it can last indefinitely. At a 4% withdrawal rate on a diversified portfolio, historical data suggests a 95% or higher chance of surviving a 30-year retirement. You can estimate the depletion year by modelling annual growth minus annual withdrawals until the balance reaches zero.