Methodology
Every AllFundly calculator uses standard, publicly documented financial formulas. This page lists each one, explains the assumptions, and links out to authoritative sources so you can verify the math yourself.
Compound interest
Compound interest is computed with the standard formula A = P × (1 + r/n)n·t, where P is the principal, r is the annual rate as a decimal, n is the number of compounding periods per year (daily = 365, monthly = 12, quarterly = 4, yearly = 1), and t is the number of years. Reference: SEC Investor.gov.
Savings growth with monthly contributions
The savings growth calculator extends compound interest with regular monthly deposits. Each month it adds your contribution to the running balance, then applies the monthly equivalent of the APY you entered: rm = (1 + APY)1/12 − 1. The total balance after m months is the iterated sum of those monthly steps. This produces a slightly more accurate figure than the closed-form annuity formula when contributions and compounding don't align perfectly.
Emergency fund coverage
Months covered = current savings ÷ monthly expenses. The 3, 6 and 12-month coverage tiers shown in the calculator are common reference points cited by sources such as the U.S. Consumer Financial Protection Bureau; they are not recommendations.
Debt payoff (snowball / avalanche)
The debt payoff calculator simulates month-by-month payoff. Each month it accrues interest on every active debt at APR ÷ 12, applies the minimum payment to each, then directs any remaining budget to the priority debt — smallest balance first (snowball) or highest APR first (avalanche). When a debt reaches zero, its payment rolls onto the next priority debt, growing the “snowball” over time. The simulation runs for at most 80 years to keep pathological inputs from looping.
Retirement / 401(k) projection
The retirement calculator runs a year-by-year simulation. Each year your salary grows by the raise rate, your contribution and employer match are added at the start of the year, and the running balance compounds at the expected return. Results are pre-tax nominal dollars. For inflation-adjusted (real) results, subtract your inflation assumption from the nominal expected return before running the calculation. Reference: SEC Investor.gov.
What these calculators do not include
None of the calculators on AllFundly account for taxes, account fees, IRS contribution limits, market volatility (returns are constant in our model, not random), or changes in personal circumstances. They are deterministic projections based on the inputs you provide — useful for comparing scenarios, not for guaranteeing any specific outcome.
Disclaimer
AllFundly is an informational, educational tool — not financial, investment, tax or legal advice. Numbers produced by these calculators are estimates derived from the formulas above and the inputs you supply. The Site is provided "as is" without warranty of any kind. Before making any real decision about saving, investing or borrowing, consult a qualified, licensed professional and confirm figures with your own bank, broker or plan administrator. AllFundly is not affiliated with any bank, brokerage, employer or government agency, and accepts no responsibility for any decision or loss based on the output of these calculators. See our Privacy & Disclaimer for the full terms of use.
Updates
Page last reviewed: 2026-05-03. We update formulas and assumptions as needed and note changes here.