A retirement projection answers a limited question: what could a starting balance and regular contributions become under a stated return assumption? It does not establish how much retirement will cost or guarantee an investment outcome.
Choose a time horizon
Subtract your current age from your planned retirement age. Someone aged 30 who plans to retire at 60 has a 30-year saving period. Changing the retirement age changes both the number of deposits and the time available for growth.
Separate deposits from assumed growth
Start with money already reserved for retirement and enter a monthly contribution you want to model. At a zero return, a $10,000 starting balance plus $100 each month for ten years becomes $22,000: $10,000 + ($100 × 120). This simple check helps distinguish savings from investment returns.
Understand the formula
For a fixed monthly rate i, starting balance P, monthly deposit C, and n months, the projected balance is P(1+i)^n + C((1+i)^n − 1)/i. Deposits arrive at month-end. At zero interest, the calculation becomes P + Cn. FinMathly uses the entered nominal annual rate divided by 12 in this retirement model.
Compare amounts in the same dollars
Inflation changes purchasing power. To express a future balance in today’s dollars, divide it by (1 + annual inflation rate)^years. For an illustration, $100,000 ten years from now at an assumed 3% annual inflation rate is about $74,409 in today’s dollars. This is an arithmetic scenario, not an inflation forecast.
The target field in FinMathly’s retirement calculator is in today’s dollars. Compare it with the inflation-adjusted result, not the larger nominal balance. Entering a target already inflated to the retirement date would mix two different measurement bases.
Test more than one assumption
Change the return, monthly contribution, or retirement age separately to see which assumption drives the result. A constant return smooths out the market’s actual ups and downs. The model does not calculate retirement withdrawals, pension benefits, taxes, fees, or the chance of exhausting savings.
Use the estimate
Open the Retirement Savings Calculator and compare scenarios. For the general growth formula, read how compound interest works.
Sources and scope
Investor.gov: Purchasing Power. Examples and formulas on this page are educational arithmetic; no personalized saving target is prescribed.