THE NUMORIX GUIDE
How to use the Retirement calculator
Last reviewed September 14, 2026
What this calculator does
The projection grows current savings annually, adds savingsPercent of the current year's income, and then increases income by incomeIncrease for the next year.
Formula and method
The projection grows current savings annually, adds savingsPercent of the current year's income, and then increases income by incomeIncrease for the next year. At retirement, annual need is projected income times incomeNeed minus 12 times other monthly income. The target uses the entered real return, (1+r)/(1+inflation)-1, across the years of retirement; the gap is target minus projected savings when positive.
Variables and inputs
Use current age, planned retirement age, life expectancy, current pre-tax income, income increase, income needed after retirement, investment return, inflation, other monthly income, current savings, and savings percent. Ages are years, income and savings are dollars, and rate fields are annual percentages.
Worked example
If age 40 means retirement at 60 and life expectancy 80, with $60,000 income, 0% income growth, 75% income need, 0% return, 0% inflation, $20,000 saved, and 10% saving, annual contributions are $60,000 x 0.10 = $6,000. Savings at retirement are 20,000 + 20 x 6,000 = $140,000; annual need is 60,000 x 0.75 = $45,000, so a zero-return target is 20 x 45,000 = $900,000 and the gap is $760,000.
How to interpret the result
The target is a scenario for funding the stated retirement duration, not a promise that savings will last. Income growth, inflation, returns, retirement age, and other income all affect the result. A positive gap means the modeled balance is below the modeled target, not that a particular contribution plan is impossible.
Common mistakes to avoid
Keep age order chronological. Enter other income as a monthly amount because the engine multiplies it by 12. Do not use a nominal return and inflation rate from different periods without checking the resulting real return.
Assumptions and limitations
The engine uses annual deposits and a constant return and inflation assumption. It does not model Social Security rules, taxes, fees, market volatility, health costs, required minimum distributions, changing spending, or sequence-of-returns risk. The withdrawal helper on the page is a separate simplified scenario.