Why we show the math
Most calculator sites hand you a number and move on. That number is only useful if you understand where it came from — which assumptions it makes, which costs it leaves out, and how it would change if you did one thing differently. Every CalcMatters page pairs its calculator with the formula, a worked example, and the plain-English meaning of the result.
The calculators run entirely in your browser. Nothing you type is sent anywhere or stored.
What you can work out here
The calculators fall into four groups, because most money decisions fall into the same four. Mortgage and loans covers what a house actually costs: the payment, the private mortgage insurance that comes with a small down payment, and the FHA alternative. Investing covers what money does over time — compound growth, doubling time, and the contribution limits that decide how much you can put into a Roth IRA this year.
Saving and budgeting covers the other direction: how much to set aside each month to reach a target, how the 50/30/20 split works on your actual take-home pay, and how large an emergency fund your situation needs. Taxes covers what self-employed people owe and when the IRS expects it, which is the figure most often underestimated until the bill arrives.
Where the numbers come from
Tax brackets, the standard deduction, the Social Security wage base and the IRA limits are published every autumn for the following year. We take them from the IRS and the Social Security Administration, record the date they were checked, and keep them in one place. The methodology page shows exactly which figures the site is using and when they were last verified against the source.
Everything else — your income, your loan, your rate — is entered by you and calculated in your browser. Nothing is sent to a server and nothing is stored. The result you see is the result of the formula shown on the page, applied to the numbers you typed.