145 free online calculators
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50/30/20 Rule Calculator Splits your after-tax income into a simple budget using the 50/30/20 rule: 50% for needs such as housing, food and bills, 30% for wants such as eating out and hobbies, and 20% for savings and paying off debt. Enter your monthly or yearly take-home pay to see how much belongs in each category per month and per year, and optionally enter what you actually spend on needs and wants to see whether you are over or under each target. Acres to Hectares Converter Converts acres to hectares and hectares to acres for land, farm and property areas. One acre is exactly 0.40468564224 hectares, and one hectare is about 2.4711 acres. Every answer is also shown in square metres, square kilometres, square feet, square yards and square miles, so you can compare a plot listed in one system with one listed in the other. Add Days to Date Calculator Adds or subtracts days, weeks, months and years from a date to find the resulting calendar date and its day of the week. Use it to work out deadlines, due dates, expiry dates, notice periods or the date a given number of days ago. Choose calendar days, or business days to skip Saturdays and Sundays. Months are added on the calendar, so 31 January plus one month is the last day of February. Adding Fractions Calculator Adds up to five fractions or mixed numbers and shows the working. The calculator finds the least common denominator (LCD), rewrites each fraction over it, adds the numerators and simplifies the answer. You get the result as a simplified fraction, as a mixed number and as a decimal. Negative fractions are allowed, so you can also use it to subtract. Age Calculator Works out exactly how old someone is from their date of birth: in years, months and days, and as a total number of months, weeks, days and hours. By default the age is calculated for today, or you can pick any other date to find an age on a past or future day. You also see the day of the week the person was born and the date of their next birthday with a countdown in days. Age Difference Calculator Finds the age gap between two people: siblings, partners, parents and children or friends. Enter their two ages for a quick answer, or their dates of birth for an exact difference in years, months and days (plus the total in days and weeks), or just the years they were born. The result also says who is older and gives the gap as decimal years, months, weeks and days. Allele Frequency Calculator Works out allele frequencies three ways. From the prevalence of a recessive condition (as '1 in N' or a percentage) it finds the disease allele frequency q, the normal allele frequency p, the share of non-carriers, carriers and affected people, and the carrier rate as '1 in X'. From AA, Aa and aa genotype counts it counts alleles to get p, q and the minor allele frequency, and from raw allele counts it handles up to five alleles. Amortization Calculator Builds the repayment schedule for any fixed-rate loan. Enter the loan amount, the interest rate, the term and how often interest is compounded and payments are made (monthly, bi-weekly, weekly and more). You get the regular payment, the total paid, the total interest and a year-by-year amortization table showing how much of each year's payments goes to principal and to interest and what balance remains. Add an extra payment each period to see how much sooner the loan is repaid and how much interest you save.
Allele Frequency Calculator Works out allele frequencies three ways. From the prevalence of a recessive condition (as '1 in N' or a percentage) it finds the disease allele frequency q, the normal allele frequency p, the share of non-carriers, carriers and affected people, and the carrier rate as '1 in X'. From AA, Aa and aa genotype counts it counts alleles to get p, q and the minor allele frequency, and from raw allele counts it handles up to five alleles. Animal Mortality Rate Calculator Turns farm stock records into mortality figures for a herd, flock or pond over one production cycle. Enter the opening stock, animals born, animals sold and the closing stock (or the number of deaths directly) to get the number of deaths, the mortality rate as a percentage of all animals present, the survival rate and the cumulative mortality ratio. Add disease cases and disease deaths for the case mortality (case fatality) rate and the share of animals that fell ill. Annealing Temperature Calculator Finds the optimal PCR annealing temperature with the Rychlik formula Ta = 0.3 × Tm(primer) + 0.7 × Tm(product) − 14.9. Enter the melting temperature of the less stable primer and of the PCR product in °C, °F or K, or paste both primer sequences and let the calculator work out each primer's Tm (nearest-neighbour, salt-adjusted or basic method) and the product Tm from its length and GC content at your salt concentration. It also flags primer pairs whose melting temperatures differ by more than 5 °C.
Half-Life Calculator Works with exponential decay through the half-life: the time it takes for half of a radioactive isotope, a drug in the body or any decaying quantity to disappear. Give any three of initial quantity, remaining quantity, half-life and elapsed time to find the fourth. The result also shows the percentage left, the number of half-lives that have passed, the decay constant λ and the mean lifetime τ. Molar Mass Calculator Calculates the molar mass of a chemical compound. Type a formula such as H2O, Ca(OH)2, Al2(SO4)3 or the hydrate CuSO4·5H2O, or pick elements from the full periodic table (all 118) and set how many atoms of each. The calculator adds up the atomic weights and shows the molar mass in grams per mole, the number of atoms, and each element's mass contribution and percentage by mass. Molarity Calculator Calculates the molarity of a solution, or works backwards to the mass of solute or the volume of solution you need for a target molarity. Molarity is the amount of dissolved substance in moles per litre of solution (mol/L, written M). Enter the molar mass with the mass of solute and the final volume, a target molarity, or a mass concentration in g/L, and get the molarity, moles of solute and concentration.
Board Foot Calculator Calculates board feet, the unit used in the United States and Canada to measure and price lumber. One board foot is 144 cubic inches (1 in × 12 in × 12 in). Enter the thickness and width in inches and the length in feet (or millimetres and metres), how many boards you have, an optional waste allowance and the price per board foot, to get the board footage per board, the total, the quantity to order, the volume in cubic feet and cubic metres, and the cost. Brick Calculator Estimates how many bricks you need for a wall. Work in metric (metres and millimetres) or imperial (feet and inches), enter the wall length and height or its area, deduct doors and windows, and give the brick size, mortar joint and wall thickness (half-brick or one-brick). The calculator returns the net wall area, bricks per unit area, the bricks required, the quantity to order with a waste allowance, the wet volume of mortar and, optionally, the cost of the bricks. Concrete Slab Calculator Calculates the volume of concrete for rectangular slabs, footings and walls or for round columns and post holes. Choose imperial (feet and inches, result in cubic yards) or metric (metres and centimetres, result in cubic metres), enter the dimensions and how many identical pours you need, and add a waste allowance. If you use pre-mixed bags, enter the concrete density and bag weight to get the total weight, the number of bags and their cost.
Acres to Hectares Converter Converts acres to hectares and hectares to acres for land, farm and property areas. One acre is exactly 0.40468564224 hectares, and one hectare is about 2.4711 acres. Every answer is also shown in square metres, square kilometres, square feet, square yards and square miles, so you can compare a plot listed in one system with one listed in the other. Binary Converter Converts whole numbers between decimal and binary, including negative numbers stored as two's complement, the way computers hold signed integers. Choose the word size (4 to 64 bits) to see the exact bit pattern, the range of values that size can hold, and the same number in hexadecimal and octal. In the other direction, paste a bit pattern to read it both as an unsigned number and as a signed two's-complement number. Byte Converter Calculator Converts between bits and bytes and every decimal and binary multiple of them: kilobytes, megabytes, gigabytes and terabytes in powers of 1000, and kibibytes, mebibytes, gibibytes and tebibytes in powers of 1024, up to yottabytes and yobibytes. It explains why a 1 TB drive shows up as about 931 GB in some operating systems, and turns network speeds in megabits into file sizes in megabytes. Each result is also given in bytes, bits and the best-fitting decimal and binary unit.
Add Days to Date Calculator Adds or subtracts days, weeks, months and years from a date to find the resulting calendar date and its day of the week. Use it to work out deadlines, due dates, expiry dates, notice periods or the date a given number of days ago. Choose calendar days, or business days to skip Saturdays and Sundays. Months are added on the calendar, so 31 January plus one month is the last day of February. Age Calculator Works out exactly how old someone is from their date of birth: in years, months and days, and as a total number of months, weeks, days and hours. By default the age is calculated for today, or you can pick any other date to find an age on a past or future day. You also see the day of the week the person was born and the date of their next birthday with a countdown in days. Age Difference Calculator Finds the age gap between two people: siblings, partners, parents and children or friends. Enter their two ages for a quick answer, or their dates of birth for an exact difference in years, months and days (plus the total in days and weeks), or just the years they were born. The result also says who is older and gives the gap as decimal years, months, weeks and days.
50/30/20 Rule Calculator Splits your after-tax income into a simple budget using the 50/30/20 rule: 50% for needs such as housing, food and bills, 30% for wants such as eating out and hobbies, and 20% for savings and paying off debt. Enter your monthly or yearly take-home pay to see how much belongs in each category per month and per year, and optionally enter what you actually spend on needs and wants to see whether you are over or under each target. Amortization Calculator Builds the repayment schedule for any fixed-rate loan. Enter the loan amount, the interest rate, the term and how often interest is compounded and payments are made (monthly, bi-weekly, weekly and more). You get the regular payment, the total paid, the total interest and a year-by-year amortization table showing how much of each year's payments goes to principal and to interest and what balance remains. Add an extra payment each period to see how much sooner the loan is repaid and how much interest you save. APR Calculator Finds the annual percentage rate (APR) of a loan: the yearly cost of borrowing once fees are included, not just the quoted interest rate. Enter the loan amount, interest rate, term, payment and compounding frequency, and any fees, whether they are added to the loan or paid separately up front. The calculator works out the regular payment and then the rate at which those payments exactly repay the money you actually receive, giving the APR, the effective annual rate and the total cost of the loan.
Blood Alcohol Content (BAC) Calculator Estimates your blood alcohol content (BAC) with the Widmark formula from your sex, body weight, what you drank and how long ago you started drinking. Count beers, large beers, glasses of wine and shots, or enter grams of alcohol directly. The result shows your estimated BAC in percent and per mille, how it compares with the drink-driving limit where you are, and roughly how long until it falls below the limit and back to zero. It is an estimate only: never use it to decide whether you can drive. BMI Calculator Work out your body mass index (BMI) from your height and weight in metric or imperial units (cm, m, feet and inches, inches, kg, pounds, stones). The result shows the WHO adult weight category, BMI Prime, the ponderal index, the healthy weight range for your height and how much weight you would need to gain or lose to reach it. Add your age and sex to see where your BMI sits among US adults of the same age and sex. BMR Calculator (Basal Metabolic Rate) Estimates your basal metabolic rate: the energy your body burns in a day at complete rest to keep you breathing, warm and alive. Choose from five published prediction equations (Mifflin-St Jeor, the original and revised Harris-Benedict, Katch-McArdle and Schofield), enter your sex, age, height and weight in metric or imperial units, and get your BMR in kcal and kJ per day. Add your activity level to see your total daily energy expenditure, and optionally see roughly how that resting energy is shared between your organs.
Adding Fractions Calculator Adds up to five fractions or mixed numbers and shows the working. The calculator finds the least common denominator (LCD), rewrites each fraction over it, adds the numerators and simplifies the answer. You get the result as a simplified fraction, as a mixed number and as a decimal. Negative fractions are allowed, so you can also use it to subtract. Area Calculator Finds the area of 2D shapes: rectangle, square, triangle (from base and height, three sides, two sides and the angle between them, or two angles and the side between them), circle, semicircle, circular sector, ellipse, trapezoid, parallelogram (three ways), rhombus (three ways), kite (two ways), regular pentagon, hexagon and octagon, annulus (ring), any quadrilateral from its diagonals and any regular polygon. Pick the shape, enter its dimensions in any length unit (angles in degrees or radians), and you get the area in that unit squared, plus square metres and square feet, and the perimeter where the inputs fix it. Handy for working out the area of a room, a garden bed or a patio before buying flooring, mulch or bricks. Area of a Circle Calculator Finds the area of a circle from its radius, diameter or circumference, and works backwards from a known area to the radius. All four measurements are shown together, so you can use it for a round table top, a pizza, a garden bed, a pipe cross-section or a circular room. Pick the length unit and the area comes out in the matching square unit, also converted to square metres and square feet.
Calculators for everyday decisions
MyKalculators is a free collection of online calculators. Every calculator is checked against independent references before it is published, and shows the formula and a worked example on the same page.
Every calculator runs entirely in your browser. Your numbers never leave your device, results update instantly as you type, and the whole site works on mobile data. Calculators that rely on tax rates or government fees show when they were last reviewed and link to their sources, so you can verify the figures before you rely on them.