Inputs and assumptions
Simuily calculates educational scenarios from your inputs. It does not automatically obtain market rates, future inflation, property prices or lender terms. Defaults are editable examples. Country, language and currency are independent; changing currency does not perform an exchange-rate conversion.
Savings and contributions
The savings model uses a constant effective annual rate. Its monthly equivalent is (1 + annual rate)^(1/12) − 1. Each month applies growth to the balance before adding the contribution. Contributed money is starting capital plus contributions. Growth is the difference between the balance and contributed money.
Purchasing power divides a future balance by (1 + annual inflation)^years. This is a general price assumption, not a prediction for a particular item. Zero interest is calculated as a simple sum of contributions, avoiding division by zero.
Savings targets
The target is entered at today’s prices and grows with the stated inflation assumption. The required contribution reaches that future target over the selected term using the same end-of-month convention. An assumed return is not a guarantee.
Mortgage payments
The constant payment is P × i / [1 − (1 + i)^(-n)], where P is principal, i the monthly rate and n the payment count. At zero interest it is P / n. Rate conventions include nominal annual divided by twelve, effective annual converted to monthly, and nominal annual with semiannual compounding converted to monthly. Select the convention in your contract.
The schedule covers principal and interest. Insurance, recurring taxes and other expenses are manual monthly budget inputs and do not enter the amortisation schedule. The model excludes rate resets and interest-only loans.
Early repayment
Scenarios start from the current outstanding balance. The extra payment reduces principal. Keeping the term and lowering the payment is compared with retaining the payment and shortening the term. The final payment adjusts to the remaining balance. Net savings subtract the entered charge from future interest avoided. Taxes, deductions and alternative investments are excluded.
Home purchases and countries
Upfront cash combines the down payment, manual costs and reserve. The loan is the price minus the down payment. This does not establish that a lender will approve financing. Costs must be checked for the relevant country, region, property and buyer. Official resources for Spain, the United States, the United Kingdom and Canada are linked within the tools. Other markets retain a general model with manual cost inputs.
Tables, rounding and calculation privacy
The engine uses floating-point precision and displays money rounded to two decimal places. Small differences can arise when adding already rounded figures. Yearly tables are open and the CSV includes inputs and assumptions. Calculations run in the browser: the plugin does not send financial amounts to the server. Site search does send the query text to locate pages and articles.
Emergency fund
No interest, inflation or withdrawals. The coverage target is your choice, not a recommendation.
target = expenses × months; missing = max(0, target − available); time = ceil(missing / monthly)
Investment fees
Annual fee converted to an equivalent monthly deduction after growth, before the contribution. No tax or trading costs.
d = 1 − (1−fee)^(1/12); balance(m) = balance(m−1) × (1+i) × (1−d) + contribution
Borrowing capacity
This is a mathematical payment limit, not lender approval. Enter a payment after other household costs.
principal = payment × (1 − (1+i)^(−months)) / i; i=0: principal=payment×months
Symbols, zero-rate cases and limits
P: initial principal; A: monthly contribution; n: number of months; t: years; r: annual rate as a decimal; π: annual inflation as a decimal; i: monthly rate; G: target at current prices; E: essential monthly expenses; M: coverage months; S: available savings; C: monthly payment; f: annual fee as a decimal; d: equivalent monthly deduction. Inputs use percentages: 5% becomes 0.05 in the formulas.
At zero interest the target contribution is max(0, (G × (1+π)^t − P) / n). Emergency-fund time is zero if the target is already covered; a remaining shortfall cannot be closed with zero contributions under this model.
Cash for a purchase is down payment + manual costs + reserve. The loan is price − down payment. Overpayments compare three monthly schedules: baseline, lower payment and shorter term. Avoided interest starts on the same date and the entered fee is deducted. Future rate resets, tax relief and recurring extra payments are not included.
Discount calculator
Successive discounts multiply: 20% followed by 10% equals 28%, not 30%. Three-for-two removes the price of one item for each complete group of three identical items. Leftover items are charged in full. A second-item discount applies once per complete pair. Each row is an alternative offer; offers are not combined with each other.
All items are assumed to have the same price. The model excludes cheapest-item discounts in mixed baskets, minimum-spend coupons, delivery charges and redemption limits. Use final tax-inclusive prices and check the retailer’s conditions. Rounding is applied to displayed totals; a retailer may round each receipt line.
Unit price comparison
The reference price is the total price divided by the amount per pack, the pack count and the conversion factor. For example, 500 g at 3 costs 6 per kg; 750 g at 4.20 costs 5.60 per kg. The difference is 0.40 per kg. Grams, kilograms, ounces and pounds compare mass; millilitres, litres and fluid ounces compare volume.
Weight is not converted to volume: one litre is not necessarily one kilogram. Mass ounces, US fluid ounces and Imperial fluid ounces are distinguished. Compare equivalent products and enter the price of the complete multipack, not one pack when you have entered several. Waste, quality, transport and nutritional value are not calculated.
Trip cost calculator
Fuel volume equals total distance multiplied by litres per 100 km, divided by 100. The equivalent price per litre is then applied. A 300 km trip at 6 L/100 km and 1.60 per litre uses 18 litres and costs 28.80 in fuel. Other expenses are added once for the complete journey.
Distance is not retrieved from a map and current fuel prices are not fetched. Use your car’s observed consumption when available. Return mode doubles distance but not extra expenses: enter tolls and parking for the whole journey. Wear, insurance, depreciation and meals are not added automatically.
Petrol and electric car comparison
Each year’s cost is the purchase price plus accumulated annual expenses; the electric car adds the charger upfront. Grid energy equals battery consumption divided by charging efficiency. At 15,000 km a year, 16 kWh/100 km and 90% efficiency, approximately 2,666.67 kWh from the grid is needed. At 0.25 per kWh, electricity alone costs approximately 666.67 a year.
This compares cash outlays, excluding resale value, financing, inflation and opportunity cost. Insurance, maintenance and taxes are included only if entered as other costs. If electric consumption is already measured at the plug, use 100% efficiency to avoid double-counting losses. No subsidies or country tariffs are assigned, and range is not estimated.
Electricity cost calculator
Daily active energy is watts × hours ÷ 1,000. Standby energy uses 24 hours minus active hours, avoiding double-counting time. Multiply by days, number of devices and price per kWh. A 1,000 W device used two hours daily for 30 days consumes 60 kWh; at 0.25 per kWh it costs 15, excluding standby.
This is not a full electricity bill: it excludes fixed service charges, separately billed taxes and time-of-use bands. Enter an appropriate final kWh price for the operating hours. Rated power may differ from average consumption for thermostatic or cycling appliances. For those, measured data or annual label consumption in the replacement tool is preferable.
Appliance replacement calculator
Annual savings equal the consumption difference times the kWh price, plus the difference in other annual costs. Simple payback is replacement cost divided by positive annual savings. Moving from 500 to 250 kWh/year at 0.25 saves 62.50 a year in energy. A replacement cost of 500 gives an eight-year simple payback if other costs are equal.
Financing, inflation, future failures, resale value and changes in usage are excluded. Label consumption comes from test conditions and may differ from actual use. Include installation and disposal in net cost when applicable. Payback beyond expected useful life does not establish that replacement is worthwhile. Without positive annual savings, no finite savings-based payback is shown.