The math, shown.
What Abacus is for.
Abacus has five calculators for big money decisions: buying a home, taking a loan, investing for the long run, planning retirement, and choosing between renting and buying. Each one shows its working. You get the payment or balance, the formula behind it, a year-by-year table, and a sensitivity strip that shows how far the answer moves when one assumption changes.
The math runs in your browser. Your inputs are saved in your browser’s local storage on this device, so they are still there when you come back. Your numbers don’t go to a lender, and there is no form asking for your email before you see a result.
These are planning tools, not quotes. They assume fixed rates and steady returns, and they leave out income taxes, lender fees, and anything else a real offer adds. Use them to compare options and find the assumption that swings the result. Then confirm the real numbers with your lender or a tax professional.
Which tool to open
Questions people ask.
What does PITI mean?
Principal, interest, taxes, and insurance: the four parts of a typical monthly mortgage payment. Lenders look at the full PITI figure, not just principal and interest, when they decide what you can borrow. The Mortgage Calculator shows each part on its own line, plus HOA dues and PMI when they apply.
How much does paying extra principal save?
It depends on the rate and how early you start, so the Mortgage and Loan calculators run the schedule twice, with and without your extra amount, and show the difference in interest and months. Extra principal early in a loan saves the most, because that is when most of each payment goes to interest.
What is the 4% rule?
A rule of thumb from 1990s retirement research: withdraw 4% of your portfolio in the first year, raise the amount with inflation each year after, and the money historically lasted 30 years. It is a starting point, not a guarantee. For retirements longer than 30 years, many planners use 3.5% or less. The Retirement Calculator lets you set your own rate.
Is it better to rent or buy?
It depends on how long you stay, how fast prices and rents rise, and what a renter’s spare cash would earn invested. Buying has big costs to get in and get out, so short stays usually favor renting. The Rent vs Buy calculator finds the break-even year for your numbers and shows how much it shifts if home prices grow faster or slower than you guessed.
Do these calculators include taxes?
Property tax, yes, where it belongs in a housing cost. Income tax, no. They don’t apply mortgage interest deductions, tax on retirement withdrawals, or tax on investment growth. The one exception is Rent vs Buy, which applies a capital gains rate to the renter’s portfolio when you exit.