About Plainsum

Plainsum is a set of free financial calculators for everyday money decisions: buying a home, paying off a loan, saving for retirement and estimating taxes.

Why we built it

Most calculator sites haven't changed in years. They make you press Calculate after every change, hide the assumptions, and leave you with a table of numbers and no explanation. Plainsum updates as you type, points out what matters (like when your PMI ends, or employer match you're missing), and shows the formula and assumptions behind every result.

How we keep the math right

• Loan schedules round to the cent each month, the way lenders do, so they match real statements.
• Tax figures use the official IRS numbers for 2026 and are updated each year.
• Every calculator is tested against independent formulas and known reference results.

If you spot something that looks wrong, please tell us. We read every message.

Not financial advice

Plainsum gives estimates to help you plan. It doesn't know your full situation and isn't financial, tax or legal advice. For big decisions, talk with a qualified professional.