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Express how many standard deviations an observation lies above or below a mean. Standard deviation must be positive.
Estimate the standard error of a sample mean for independent observations. Correlated sampling may require a different model.
Compare relative spread on a ratio scale with a positive mean. This measure is not appropriate for arbitrary-zero scales such as Celsius.
Measure linear association in paired observations. Both series need equal length and nonzero variance; correlation does not establish causation.
Find the probability of exactly k successes in independent trials sharing a fixed success probability between zero and one.
Estimate the probability of exactly k events under a Poisson model with a constant rate and independent occurrences.
Calculate interest on the original principal only. The annual rate stays fixed; fees, taxes and inflation are excluded.
Project a balance with a fixed nominal rate and regular compounding. No contributions, withdrawals, taxes or fees are included.
Convert a nominal annual rate to an effective annual rate using the stated compounding frequency. This excludes fees.
Find a compounded monthly rate equivalent to an effective annual rate. Dividing the annual percentage by twelve is not equivalent compounding.
Discount one future payment to today using a fixed annual rate. The rate and horizon must use consistent annual periods.
Value equal payments made at the end of each period. At zero interest, present value equals the sum of payments.
Project equal contributions deposited at the end of each period. Contributions and return rate must refer to the same period.
Find a monthly contribution needed to close a savings gap without assuming investment returns or inflation.
Calculate equal monthly principal-and-interest payments for a fixed-rate loan. Fees and insurance are excluded.
Estimate remaining principal just after the kth scheduled monthly payment. Assumes no extra payments, missed payments or fees.
Estimate one monthly interest-only payment. This payment does not reduce principal and does not include fees.
Measure net return relative to the total invested cost. This does not annualize the return or account for cash-flow timing.
Find a constant annual growth rate between two positive values. Intermediate deposits and withdrawals are excluded.
Adjust a nominal return for inflation over the same time period. Both rates are entered by you, not retrieved live.
Estimate future purchasing power of an unchanged cash amount under a constant assumed inflation rate.
Calculate the exact time to double under constant annual compound growth. This is a projection, not a promise of return.
Measure profit as a percentage of revenue. Include every cost relevant to the margin you intend to measure.
Set a selling price by adding a percentage of cost. Markup on cost differs from profit margin on revenue.
Find whole units needed to cover fixed costs. Selling price must exceed variable cost per unit.
Compare packages by cost per unit of quantity. Use the same unit, such as kilograms or pieces, for every package compared.
Apply a second discount to an already discounted price. Discount percentages cannot simply be added.
Allocate depreciable cost evenly over useful life. Salvage cannot exceed cost; this is a general model, not a local tax schedule.
Estimate simple payback with constant annual cash flows. It ignores discounting and cash flows after recovery.
Compare an entered annual dividend with an entered share price. Dividend amounts may change and no live market data is used.
Compute a price-to-earnings ratio for positive earnings. Ensure price and earnings refer to the same share basis and currency.
Subtract outstanding liabilities from asset values measured at the same date. This does not assess liquidity or future income.
Calculate a reserve target using the number of months you choose and subtract existing savings. The tool does not prescribe a target.
Convert annual gross pay to an hourly equivalent based on paid hours. Taxes, overtime premiums and benefits are excluded.
Estimate gross overtime pay using a multiplier you provide. This does not determine statutory eligibility or local labor rules.
Convert money with an exchange rate entered manually and a percentage fee. No live rate or bank quotation is retrieved.
Divide total distance by total elapsed time, including stops. This is average speed, not instantaneous speed.
Calculate average acceleration along one axis. Signed velocities must refer to the same positive direction.
Calculate displacement and final velocity under constant acceleration in one dimension. Displacement may differ from total distance.
Estimate fall time and speed from rest with constant gravity and no air resistance. Real objects may behave differently.
Estimate an ideal projectile range when launch and landing heights match. Air resistance, wind and curvature are excluded.
Calculate net force from mass and acceleration in SI units under classical mechanics.
Calculate classical translational kinetic energy. The model is intended for speeds far below the speed of light.
Calculate gravitational potential energy relative to a chosen height reference, assuming constant local gravity.
Calculate signed linear momentum along one axis. Mass is nonnegative and velocity sets the direction.
Calculate impulse using average force over a time interval. It equals the change in momentum along the same axis.
Calculate work by a constant force along a straight displacement. Perpendicular forces do zero work in this model.
Find average power from work transferred during a positive time interval. The result is watts when inputs are joules and seconds.
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Everyday money
Separate price, tax, fees and repayments with the calculator that matches your transaction. Compare scenarios using the same currency and cost basis.
Investing
Choose a one-time investment, regular contributions or deposit model that matches your cash flows. Compare total contributions alongside projected value.
Pay & work
Choose gross pay conversion or the country-specific payroll calculation that matches your question. Read the pay period and deductions included in the result.
Housing & loans
Compare loan payments and broader housing costs using separate amounts. Keep the financed principal and rate constant when testing another term.
Maths
Choose the operation that matches your percentage, ratio or equation problem. Match each symbol in the formula to the example input.
Dates & age
Choose elapsed days, calendar position or completed age according to your question. Date conventions matter at month ends and around leap days.
Unit converters
Select the quantity, then choose its source and destination units. Read variant names before converting units with similar labels.
Geometry
Choose a shape and enter the dimensions its formula requires. Check whether each label asks for a radius, diameter, perpendicular height or semiaxis.
Statistics
Choose the measure that matches your question about centre, spread or probability. Sample estimates, population measures and probability models use different assumptions.
Physics
Choose the physical quantity you want to find and supply the units required by its equation. Read the model assumptions before applying the result to a real system.
Home & construction
Estimate material quantities or project costs from measured dimensions. Choose the tool matching the material and measurement before comparing prices.