from a guy who stares at spreadsheets all day • Updated regularly-ish
Calculators for loans, taxes, bookkeeping & pay — with the spreadsheet
Run the numbers here, then download an Excel file that does the same math with real formulas. 38 of them so far, all free, and nothing you type ever leaves your browser.
Explore by topic
- Loans & DebtPayments, payoff dates, refinancing, recasts, and the accounting side of debt.11 calculators
- Assets & DepreciationDepreciation (book and MACRS), disposals, prepaids, and what actually goes on the balance sheet.6 calculators
- Business & PricingBreak-even, margins, pricing, what an employee really costs, and a sanity check on valuation.8 calculators
- TaxesEstimated payments, self-employment tax, Section 179, recapture, and installment sales.6 calculators
- Work & PaySalary vs. hourly vs. contractor, overtime, shift differentials, back pay, PTO, and job offers.7 calculators
Good places to start
All 38 calculators ⟶- Loans
Loan Amortization
Your payment, the total interest, and every single payment split into interest and principal — plus a live Excel schedule you can poke at.
Open calculator - Tax
Self-Employment Tax
The Social Security and Medicare tax you pay as your own boss, figured line by line like Schedule SE — including a W-2 job's effect on the wage base, the Additional Medicare Tax, and how much to set aside.
Open calculator - Tax
Estimated Tax Safe Harbor
The least you can pay in estimated taxes and still owe no underpayment penalty — which rule you're under, what's left after withholding, and what to send each quarter.
Open calculator - Work & Pay
Salary to Hourly
Turn a salary into an hourly rate (or the other way around) — plus what you really make per hour worked once time off and overtime are counted, and what each paycheck comes to.
Open calculator - Business
Break-Even Point
How many units you have to sell before you stop losing money — plus your margin of safety, what it takes to hit a profit goal, and profit at different sales levels.
Open calculator - Assets
MACRS Depreciation
Tax depreciation straight from the IRS tables: every property class, half-year or mid-quarter, rental and commercial buildings by month, with §179, bonus, business use, and the year you sell.
Open calculator
Why every calculator comes with a spreadsheet
Most calculator sites hand you a number and ask you to trust it. I’d rather you didn’t have to.
Check my math
The spreadsheet does the same math with live formulas — PMT, ROUND, the whole trail — not pasted numbers. If I got something wrong, you'll see it.
Change it
The yellow cells are inputs. Change one and everything downstream recalculates, so you can try what-ifs without coming back here.
Keep it
Save it with your records, send it to your accountant, or drop it in a workpaper. Every file says what it assumes and where its numbers come from.
How I keep these honest
Tested against the source
Answers are checked against IRS forms and tables, the Labor Department’s own overtime examples, and Excel’s financial functions. How the math works
The spreadsheet matches the site
Every workbook’s formulas are recalculated in testing and have to match the website to the cent.
Dated and versioned
Each calculator shows when I last reviewed it. Tax numbers are tied to a tax year and cite where they come from.
Corrections out loud
Spot an error? Tell me. Fixes get a new version and a line in the changelog.