Purpose and steps
Future savings = current savings × (1 + monthly return)^months + monthly deposits × annuity factor. Target = today’s monthly spending × inflation factor × 12 / annual withdrawal rate. The calculation runs locally and keeps cash-flow timing consistent with the stated assumptions.
- Confirm currency and monthly versus annual amounts. U.S. tax and loan models should be used within their stated scope.
- Prepare Current age, Retirement age, Current retirement savings, Monthly contribution, Expected annual return, Annual inflation, Monthly retirement spending in today’s dollars, Annual withdrawal rate. Defaults demonstrate the model rather than your personal circumstances.
- Check the headline result and its components. A key interpretation for this tool is: The projected balance is nominal; today’s-dollar balance allows comparison with current living costs.
- Compare the baseline with a changed scenario: The withdrawal percentage is a scenario input, not a promised safe rate.
Input reference and units
These values reproduce the model’s demonstration. Replace them with your own records or measurements; they are not recommended targets.
On a small screen, swipe the table horizontally to see all columns.
| Parameter | Demonstration value | How to enter it |
|---|---|---|
| Current age | 30 age | Use completed years of age; this is not a duration field. |
| Retirement age | 65 age | Use completed years of age; this is not a duration field. |
| Current retirement savings | 50000 USD | Use dollars and the monthly or annual period stated in the field label; do not enter thousands of dollars. |
| Monthly contribution | 500 USD | Use dollars and the monthly or annual period stated in the field label; do not enter thousands of dollars. |
| Expected annual return | 7 % | A scenario assumption, not a promised investment yield; also test a lower return. |
| Annual inflation | 3 % | Enter a percentage such as 6.5, not 0.065. The equation converts it to a decimal. |
| Monthly retirement spending in today’s dollars | 3000 USD | Use dollars and the monthly or annual period stated in the field label; do not enter thousands of dollars. |
| Annual withdrawal rate | 4 % | Enter a percentage such as 6.5, not 0.065. The equation converts it to a decimal. |
Model-specific method
How this calculator produces its result
Future savings = current savings × (1 + monthly return)^months + monthly deposits × annuity factor. Target = today’s monthly spending × inflation factor × 12 / annual withdrawal rate.
Geometric growth and a stream of contributions
Compound growth multiplies the previous balance, including earlier interest, by the next period’s growth factor. The contribution term is another geometric sum: the first deposit compounds for longer than the last. It applies only to equal deposits and a constant rate; growing contributions require a different sum or period-by-period simulation.
A nominal rate compounded m times per year has effective annual growth (1+j/m)^m−1. An already effective annual return converts to a monthly rate as (1+g)^(1/12)−1. These are different conventions, so use the one specified by the tool. A constant return model says nothing about volatility or sequence-of-returns risk.
FV = P(1+r)^n FV of end-period deposits = C × ((1+r)^n − 1)/r Beginning-period deposits multiply the deposit term by (1+r)
- P: initial amount
- C: equal contribution per period
- r: growth rate for that period
- n: periods, with contributions and growth on the same schedule
Worked example
A $3,000 monthly spending target in today’s dollars is $36,000 a year. At a 4% withdrawal assumption it implies $900,000 in today’s dollars, before inflating the target to retirement.
Reproduce the default scenario
This is a separate example, calculated using the exact engine on the tool page and the defaults in the input reference above. Health examples use metric units. Displayed rounding may differ from intermediate precision.
- Projected retirement balance
- 1,475,834.89 USD
- Balance in today’s dollars
- 524,487.22 USD
- Inflation-adjusted savings target
- 2,532,476.21 USD
- Projected surplus / shortfall
- -1,056,641.32 USD
- Extra monthly contribution needed
- 586.68 USD
- Monthly withdrawal in today’s dollars
- 1,748.29 USD
- Total contributions
- 260,000 USD
- Projected investment growth
- 1,215,834.89 USD
Reading results without overstating them
- The projected balance is nominal; today’s-dollar balance allows comparison with current living costs.
- The withdrawal percentage is a scenario input, not a promised safe rate.
Assumptions and exclusions
- Assumes a constant return, month-end deposits and no tax or fees. Social Security, pensions, changing savings limits and market sequence risk are excluded; funds lasting through retirement are not guaranteed.
Sources and content notes
Toolify describes the implemented algorithm and its assumptions. Sources below support the topic or applicable rules; they do not endorse this calculator. Examples are illustrative, and published rules take precedence over simplified estimates.
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