Methodology and Sources

Last reviewed 2026-10-22.

Savings and compound interest

The annual rate is converted to a monthly rate: (1 + rate / n)^(n / 12) - 1, with n compounding periods a year.
Each month: balance = balance x (1 + monthly rate) + deposit. For deposits at the start of the month, the deposit is added first.
Years are rounded to whole months.

Deposit = (goal - current x (1 + i)^N) x i / ((1 + i)^N - 1), where i is the monthly rate and N is the number of months.

APY = (1 + APR / n)^n - 1.

Monthly contributions are salary / 12 x your percentage. The match is the match rate x the smaller of your percentage and the match cap, as a percent of salary.
The monthly return is (1 + yearly return)^(1/12) - 1. Salary rises once a year by the increase you enter.
The 2026 employee deferral limit of $24,500 and catch-up amounts of $8,000 (age 50 and over) and $11,250 (ages 60 to 63) are from the IRS announcement of November 2025 as reported by Axios. Check IRS guidance for the current year.

Maximum rent = monthly gross income x the share you choose, 30% by default. The 40 times rule multiplies the monthly rent by 40.

Payment = P x i / (1 - (1 + i)^-N), with i the monthly rate and N the months.
Break-even months = closing costs / monthly savings, shown only when costs are paid up front and the payment falls.
Interest = payment x months - principal for each loan. Closing costs paid up front are not subtracted.
If you enter your actual payment, that is used instead of the calculated one.

Taxes, fees, inflation, changes in rates, and mortgage taxes, insurance and PMI.

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