Separate asset-target solving from retirement adequacy
The four modes share one accumulation model. A nominal asset target is your input, not a number inferred from spending. Meeting it does not establish that retirement is affordable. The withdrawal schedule provides a separate constant-return spending scenario.
Know the solver boundaries
Monthly Savings returns zero if existing assets already reach the target, otherwise it solves the linear contribution requirement. Retirement Age checks every whole age through 100, avoiding an assumption that balances always rise when returns are negative. Required Return searches 0–100% nominal annual rates and reports no solution when the target is unreachable within that range. A high solved rate is not an attainable-return recommendation.
Apply one currency and timing convention
All amounts use USD. Accumulation contributions occur at month-start. The chosen nominal rate and compounding frequency are converted to an equivalent monthly growth rate; this does not model a bank’s exact interest-crediting rules. The first-year deposit row contains new contributions only, with starting savings separate.
Keep nominal and real values distinct
Nominal retirement assets are divided by cumulative inflation to show today’s purchasing power. Annual spending and Social Security start in today’s dollars and rise with the inflation assumption. Retirement uses nominal effective annual returns, including losses, before year-end withdrawals. There is no minimum positive return floor.
Read shortfalls and income correctly
Fully funded years counts complete annual withdrawals before the first insufficient payment. A partial final withdrawal does not count as a fully funded year. The first-year income figure divides the actual modeled withdrawal plus assumed Social Security by 12; it is not a permanent sustainable income rate.
Check benefits and risks separately
Use a personal estimate from SSA. This model assumes benefits start at retirement and increase at the chosen inflation rate. It excludes claiming rules, taxes, fees, account limits and variable-return sequences. Review multiple scenarios instead of treating a single result as a retirement guarantee.