Stocks · Cash · Retirement income

Investment Lab

Compare a stock-and-cash portfolio with a benchmark. Explore market conditions, taxes, and retirement withdrawals using the same simulated stock movements for both accounts.

1. Your investment question

What are you comparing?

Study name

Starting balance ($)Years

Portfolio SPY (%)Benchmark SPY (%)

The rest of each account is cash. This is stock/cash, not a stock/bond portfolio. SPY is represented by a modeled total return, not live prices.

Restore allocation

2. Market & costs

Teaching scenarios, not forecasts. Bull +15%, neutral 0%, bear −15% growth tendency; each uses 18% volatility. A bull scenario can still lose money.

Annual growth tendency (%)Annual volatility (%)Cash annual interest (%)Annual inflation (%)

Annual portfolio fee (%)Applied to both accounts. Trade commissions and bid/ask spreads are excluded.

3. Dollar-cost averaging and contributions

Amount added each time ($)

EveryPeriod

Payment timing

When does the cash-holding account invest?

At the end of everyHolding period

Invests all accumulated cash, including net interest, on each chosen period-end. Any cash left before the next scheduled purchase stays cash.

Weekly schedules use 52 equal weeks per modeled year; monthly schedules use 12 equal months. These are model periods, not calendar dates. Beginning payments start now; end payments start after one full interval.

4. Retirement withdrawals

First-year spending from portfolio ($)Raise spending with inflation each year

Withdrawals occur at the beginning of each year after any same-date contribution. Timing comparisons turn withdrawals and rebalancing off to isolate when money is invested.

5. Account & taxes

Tax treatment

Interest / withdrawal tax rate (%)

Realized capital gains tax rate (%)Dividend tax rate (%)Annual dividend yield (%)Dividend income is already part of total return. We deduct its tax; we do not add the dividend return again.

Rates are editable assumptions, not calculated tax brackets. No RMDs, penalties, contribution limits, tax-loss offsets, or tax-lot selection. See the method before using tax comparisons.

6. Run & save

Simulated pathsRandom seed

Same settings, seed, and engine version reproduce the same results. Weekly contributions are processed at their scheduled times; charts show monthly balances.

Saved locally in this browser. Export a file to keep a backup or move between devices.

A question you can test

What changes when I keep some cash?

Choose SPY and cash, dollar-cost averaging, or retirement withdrawals. The Dollar-Cost Averaging study invests $500 each month and compares it with collecting the same money in cash and investing annually. Change an assumption and compare the results.

The lab executes the simulation in your browser. Results describe this model, not historical performance or a guaranteed safe withdrawal amount.

Saved runs

Up to six runs in this browser. Export runs you want to keep permanently.