Calculator Methodology

General assumptions

• Results are estimates for education, not predictions or personalized advice.
• Returns and inflation are held constant at the rates you enter. Real markets and prices vary from year to year.
• Taxes, investment fees, and account costs are not included unless a calculator has a specific input for them.
• Your inputs are processed in your browser. The public calculators don't save them to an account.

Compound Interest Calculator

The Compound Interest Calculator combines the growth of your starting balance with the future value of your recurring contributions:

• Starting balance: P × (1 + r / n)^{n × t}
• Contributions: C × [(1 + r / n)^{n × t} − 1] ÷ i, where i = (1 + r / n)^{n / m} − 1 is the effective rate per contribution period

P is the starting balance, r the annual rate, n compounding periods per year, t years, C the contribution amount, and m contributions per year. Contributions are treated as made at the end of each period. The rate is nominal: to see results in today's dollars, subtract expected inflation from the rate you enter.

Worked example: $10,000 plus $200 a month at 7%, compounded monthly for 20 years, grows to about $144,573: $58,000 of contributions and about $86,573 of growth.

Retirement Calculator

The Retirement Calculator works in today's dollars. It compares a target nest egg with your projected savings:

1. Spending gap: monthly retirement spending minus guaranteed income (such as Social Security or a pension), times 12.
2. Taxes: the gap is grossed up by your estimated tax rate on withdrawals: gap ÷ (1 − tax rate).
3. Required portfolio: the grossed-up gap ÷ your withdrawal rate.
4. Target: the required portfolio plus the safety margin you choose.
5. Real return: (1 + nominal return) ÷ (1 + inflation) − 1, known as the Fisher equation.
6. Projected savings: current savings grown at the real return, plus monthly contributions compounded monthly for your contribution years and then grown until retirement.

Worked example: $50,000 saved, 25 years to retirement, $800 a month in contributions, a 7% nominal return and 2.5% inflation (a 4.39% real return), $4,500 a month of spending with $2,000 of guaranteed income, a 12% tax rate, a 4% withdrawal rate, and a 20% safety margin. The gap is $30,000 a year ($34,091 before tax), so the target is about $1,022,727. Projected savings are about $581,708 in today's dollars, a shortfall of about $441,019.

Limits: a fixed withdrawal rate is a rule of thumb, not a guarantee that savings will last. The calculator doesn't model market sequences, required minimum distributions, changing spending, or Social Security claiming choices.

What Is a Dollar Worth Calculator

The What Is a Dollar Worth Calculator has two modes:

• Historical: amount × CPI_{to year} ÷ CPI_{from year}, using U.S. Bureau of Labor Statistics CPI-U annual averages (1982–84 = 100) for 1913 through 2025. For example, $1 in 1980 (CPI 82.4) had the purchasing power of about $3.88 in 2025 (CPI 319.6).
• Future: the nominal value is amount × (1 + growth)^years; the inflation-adjusted value uses the real rate (1 + growth) ÷ (1 + inflation) − 1. At 10% growth and 2% inflation, $1 becomes about $28.10 in 35 years, or about $14.05 in today's dollars.

CPI measures average price changes for urban consumers. Your personal inflation rate can differ based on what you buy and where you live.

Net Worth Tracker projections

The Net Worth Tracker calculates net worth as total assets minus total debts. Its projections grow each asset at the expected return for its asset class (or a custom rate) and show an optimistic and pessimistic band one standard deviation above and below, using a lognormal model where uncertainty widens with the square root of time. Optional contributions are added as a regular annual stream. Debts with a payment and interest rate follow a standard amortization schedule; debts without payment details are held constant. Projections are in nominal dollars.

Cash Flow Tracker

The Cash Flow Tracker converts every income stream and expense to a monthly amount (for example, weekly × 52 ÷ 12 and quarterly ÷ 3) and spreads once-a-year expenses across 12 months. Monthly cash flow is monthly income minus monthly expenses, including savings and debt payments. The savings rate is the monthly total of items in the Savings category divided by monthly income (after-tax income when the tax estimate is on); leftover cash flow isn't counted until it's assigned to a Savings item.

Questions or errors

If a result looks wrong, email team@networthinsights.com with your inputs and what you expected. See our corrections policy for how we handle reports.