Finance calculators that show the steps
A $2,000 weekly check with 12 percent federal withholding leaves $1,607. FICA is $153. Each calculator below runs in the browser, shows the formula it used, and works a real example in numbers.
Start with a number that is already checked
Class and first paycheck
Simple interest calculator and formula
Simple interest is principal times rate times years. It adds the same amount every year. Work a savings balance or a loan, then see why compounding is a different rule.
Hourly wage to annual salary
Turn an hourly wage into weekly and annual pay. Hours a week and weeks a year are inputs, so a part-time job and unpaid time off both show up. Educational, not a tax engine.
Paycheck calculator and FICA split
See where a paycheck goes: Social Security, Medicare, and the withholding you type. FICA is the part the formula actually fixes. Educational, not a tax engine.
50/30/20 budget split calculator
The 50/30/20 rule splits take-home pay into needs, wants and saving. Type the leftover and see the three buckets, including when housing already breaks the 50.
Net worth calculator and formula
Net worth is what you own minus what you owe, on one date. Work a household sheet, then see why two families with the same figure can sit in very different positions.
Credit utilization calculator
Credit utilisation is the reported revolving balance divided by the revolving limit. Work the ratio, the headroom, and why paying in full may still show a balance.
Emergency fund calculator: size and time
Size an emergency fund from your own essential monthly costs, then work out the deposit and how long the fund takes to build at a rate you pick.
Saving and growth
Compound interest calculator and formula
Work out what savings grow to with compound interest. Shows the formula, a worked example with monthly deposits, and why compounding frequency changes the total.
Savings goal calculator: monthly deposit
Work out what to put away each month to hit a target by a deadline. Shows the formula, three worked examples, and why money you already have cuts the deposit.
Rule of 72 calculator and doubling time
Divide 72 by the annual growth rate to see how long money takes to double. Shows the exact answer beside the estimate, and the rates where the shortcut drifts.
Inflation calculator and buying power
Work out what a sum will cost after years of inflation, what today's money will buy by then, and how much buying power a modest rate takes over a working life.
Real return after inflation calculator
Work out what a return is worth once inflation is taken out. Shows the Fisher relation, three worked examples, and why subtracting inflation gives the wrong answer.
Future value of an annuity calculator
Work out what a run of level payments grows to. Shows the annuity formula, worked examples paid at the end and at the start of each period, and what timing changes.
Present value calculator
Discount a future lump, a level payment stream, or both, at a stated rate and compounding frequency. The ordinary-annuity convention used here matches a bond coupon or a rent paid at period end.
CAGR calculator and formula
Work out a compound annual growth rate from a start value, an end value and a number of years. Shows the formula, worked examples, and why averaging yearly returns overstates growth.
APR vs APY calculator and formula
Convert between APR and APY, and see what compounding frequency does to a rate. Shows the formula, worked examples for savings and for a credit card.
Borrowing
Loan payment calculator and formula
Work out the monthly payment on a mortgage or loan, what it costs in total interest, and how each payment splits between interest and principal.
Mortgage affordability calculator and formula
Work out the largest mortgage a debt-to-income rule allows, the price it buys once your deposit is added, and how far that ceiling falls when the rate rises a percentage point.
Mortgage extra payment calculator
What an extra amount paid each month does to a mortgage: months taken off the term, interest not paid, and the point where extra principal stops covering that month's interest.
Credit card payoff calculator and formula
Work out how many months a card balance takes to clear at a fixed monthly payment, what the interest adds up to, and how much of the first payment is interest.
Car loan calculator: payment and total cost
Work out the monthly payment on a car loan, the interest it costs in total, and how a longer term lowers the payment while raising what you hand over.
Student loan payoff calculator
Work out the payment that clears a student loan over its standard term, what the interest costs in total, and how many months an extra fixed amount takes off.
Debt-to-income ratio calculator and formula
Work out your DTI from monthly debt payments and gross income. Shows the formula, front-end against back-end, and the room left under a lender limit.
Refinance break-even calculator and formula
Work out how many months of lower payments it takes to earn back the closing costs on a refinance, and whether the new loan costs more interest over its life.
PMI calculator and formula
Private mortgage insurance as a percent of the original loan, paid monthly until the amortised balance falls to 80 percent of the original purchase price.
Mortgage points calculator
What discount points cost in cash, how much they cut the monthly payment, and how many months of that saving it takes to recover the points if you keep the loan.
Work and retirement
Employer match calculator
How a 50 percent match on the first 6 percent of pay actually works, what is left on the table if you defer less, and what the match stream grows to if it is invested.
Retirement withdrawal calculator and formula
Work out how long a pot lasts at a fixed monthly withdrawal and a steady return, what is left after twenty years, and what a lower return takes off the end.
FIRE number calculator
The pile that covers a year's spending at a stated withdrawal rate, and how many years of saving at a constant return it takes to reach it from what you have now.
Investing and valuation
Price to earnings calculator
P/E is share price divided by earnings per share. Work the ratio, then the same number from market cap over total earnings. A low P/E is not always cheap.
DCF calculator and formula
Two-stage discounted cash flow: present value of an explicit forecast plus a Gordon-growth terminal value. Terminal growth has to stay below the discount rate or the perpetuity has no finite value.
Dividend discount calculator
Gordon growth prices a stock as next year's dividend over required return minus perpetual growth. The implied yield equals that gap, and growth has to stay below the required return.
Bond price calculator and current yield
Price a bond from its coupon rate, the market rate and the years to maturity, then see the current yield and why higher rates push the price below face value.
Bond duration calculator
Macaulay duration is the present-value-weighted wait for a bond's cash flows. Modified duration and DV01 then say how far the price moves when the yield moves.
Cap rate calculator
Capitalisation rate is net operating income divided by purchase price. The same income at a comparison cap gives the implied value, which is what makes two properties comparable.
Tax-equivalent yield calculator
The taxable yield that leaves the same after-tax amount as a municipal or other tax-exempt yield, at a stated federal marginal rate. State tax is a separate adjustment.
Expense ratio calculator and fee impact
Work out what a fund fee costs over time. The expense ratio comes off the rate your money compounds at, so a fraction of a percent a year adds up.
Business maths
Enterprise value and EV/EBITDA
Enterprise value is equity plus debt minus cash. Work the identity, then the EV/EBITDA multiple, on one sheet. The same bridge a deal model uses.
Unlevered free cash flow calculator
Free cash flow to the firm from EBIT, tax, D&A, capex and working capital. The unlevered cash a DCF discounts. Same bridge a deal model uses on a teaching sheet.
ROIC calculator and NOPAT split
Return on invested capital is NOPAT over invested capital. Work NOPAT from EBIT and tax, then the ratio. The number a cost of capital is compared with.
ROE calculator and formula
Return on equity is net income over book equity. Work a 15 percent sheet, then see why the same 15 percent on ROIC is a different claim with financial leverage sitting inside ROE.
Cash conversion cycle calculator
The cash conversion cycle is days sales plus days inventory, minus days payable. Work a 75 day cycle, then a negative one where suppliers fund the firm.
Interest coverage calculator
Interest coverage is EBIT divided by interest expense, the times-interest-earned ratio. Work an 8 times sheet, then see why a zero interest line is not infinity.
Unlevered beta calculator
Unlevered beta strips financial leverage out of an equity beta, assuming debt beta is zero. Work the Hamada identity, then relever at the same D/E to check it.
Offer premium calculator
Offer premium is the bid over the unaffected share price. Work a 30 percent premium, then a discount, on the close before the news leaked.
NPV calculator and net present value formula
Discount future cash flows to what they are worth today. Shows the NPV formula, the same project at 8 percent and at 12 percent, and the time-zero mistake.
IRR calculator: internal rate of return
Work out the internal rate of return on a project and test it against your cost of capital. Shows the formula, worked examples, and where IRR misleads.
WACC formula and calculator
Work out the weighted average cost of capital from the market value of equity and debt, the cost of each, and the tax relief on interest, with three worked examples.
Leverage ratio formula and calculator
The three leverage ratio formulas worked from one balance sheet: debt-to-equity, debt-to-assets and the equity multiplier, plus what a fall in asset values does to equity.
Break-even point calculator and formula
Work out how many units you have to sell to cover fixed and variable costs. Shows the break-even formula, contribution margin, a profit target and the rounding rule.
Payback period calculator and formula
Work out how long a project takes to return its own cost in cash, why the answer ignores everything after that date, and what to use instead when it matters.
Current ratio and gross margin calculator
Work out the current ratio, the quick ratio and the gross margin from a balance sheet and an income statement, and see why a good number depends on the industry.