Compound Slowly

Calculators

Small choices, long horizons.

Three simple illustrations of how money behaves over long stretches of time, each building on the last. Change any number and everything updates.

  1. Where your income goes: taxes, saving, and what's left to spend, plus pre-tax vs. Roth and Roth vs. taxable
  2. Saving and financial independence: why how much you save matters most, and what you can spend once work is optional
  3. The long game: what time and returns do to your plan

Also: should you pay down debt or invest?

Your numbers are saved in this browser only, so they're still here if you refresh or come back later.

1Where your income goes

What goes to taxes, what you save, and what's left to spend, and how saving through a 401(k) and HSA lowers your taxes. Money saved pre-tax costs you less than a dollar of spending money for every dollar saved. Roth accounts work the other way: no tax break now, but tax-free growth and withdrawals later.

Your income

Your saving

Your actual spending?

Upload a transactions export (CSV) from Monarch Money, Mint, Copilot, YNAB or your bank to see where your money actually goes each month, next to what your plan above leaves you to spend.

Your file stays on this device: it's read in your browser, never uploaded, and forgotten when you leave the page. Only each transaction's date, amount and category are used; merchant names, accounts and notes are ignored.

Your accounts or all taxable?

Your saving plan above, next to the simplest alternative: skip the 401(k), HSA and Roth accounts and invest in a regular taxable account instead, keeping the same amount to spend each month. Without the pre-tax accounts you'd pay more tax now, so there's less to invest.

Pre-tax or Roth?

Pre-tax saves you tax now; Roth saves you tax later. Which comes out ahead depends only on your tax rate today versus your tax rate when you take the money out. Your federal bracket once work is optional is set in step 2's assumptions.

Many people are in a lower bracket once work is optional, which favors pre-tax. But that assumes tax rates don't rise, and with federal debt where it is, that's a big assumption. It's why many people keep some of each.

Roth or taxable?

Money you'd invest after tax anyway can go into a mega backdoor Roth or a regular taxable account. Both start with the same dollars. The taxable account pays tax on dividends every year and on its gains when you sell; the Roth never does.

2Saving and financial independence

How much you keep matters more than almost anything else. Here's your savings rate from above next to 10%, 20% and 30% of the same income: invested until work becomes optional, then spent down, with Social Security and any pension, to the age you plan for. Already financially independent? Pick Financially independent in step 1 to plan your spending. Everything is in today's dollars.

Your timeline
Your goal

Your money

Cost basis: what you paid for your taxable investments, as a share of what they're worth now; the rest is gain, taxed when you sell. Or upload your holdings to fill these in.

Social Security

Assumptions
Your investments?

Upload a holdings export (CSV) from Altruist, Schwab, Fidelity, Vanguard or any custodian to see your asset allocation, what each part has returned historically, and what that suggests for your investment return above.

Your file stays on this device: it's read in your browser, never uploaded, and forgotten when you leave the page. Only each holding's ticker, name and value are used; account numbers, quantities and prices are ignored.

Once work is optional, your savings keep growing while you draw them down, and spending rises with inflation. Each year's withdrawal covers what Social Security, a pension and self-employed income (consulting, a small business, part-time work) don't, plus the tax on it: pre-tax money at your bracket once work is optional, gains in a taxable account at capital-gains rates, Roth not at all. Slide "Plan to age" to see what living longer does. Nobody knows future inflation; 3% is roughly the long-run U.S. average.

Chance of success (Monte Carlo)?

The plan above assumes the same return every year. Real markets swing, and a bad decade right after work becomes optional hurts the most. This runs 2,000 possible futures, each with its own random yearly returns around your expected return and volatility, and counts how often your money lasts.

What you could spend, by confidence

Monthly spending in all (savings plus Social Security and other income, after tax) that lasts to your plan-to age in that share of the 2,000 futures, with the first year's withdrawal rate under it. Higher confidence means less to spend.

Withdrawal rate by age

Each year's spending from savings as a share of what's left. Steady or falling means the money is keeping up; climbing means it's running down.

Sequence of returns: when bad years hit

One typical future's returns, replayed three ways with the same spending. All three average exactly the same return; only the order changes.

A concentrated stock position?

A lot of your money in one company's stock, from equity compensation, a founder's stake or an old holding, can grow fast or fall hard. Selling it lowers that risk but costs capital-gains tax. This compares keeping it, selling it gradually, and selling it all as soon as you can, in the same 1,000 possible futures, with your savings, spending and Social Security from above.

The position

Don't include it in "Taxable investments" above. A single stock typically swings 30% to 50% a year, two to three times as much as a diversified portfolio. "Moves with the market" is its correlation with your other investments.

The plan

"Can't sell for" covers a lockup (often 6 months after an IPO), vesting or a trading window, in quarters. "Sell each year" is a share of what you still hold, so each year's sale is smaller. "Keep for the long run" is a share of today's shares you hold on to either way.

Your investments in a bad future

In all, the stock included, where 1 in 10 futures do worse. Selling gradually trades some upside for a higher floor.

Your plan, year by year

At the expected returns, in today's dollars.

Rent or buy a home?

Buying costs more up front and builds equity; renting keeps that money invested. This finds how long you'd need to stay for buying to come out ahead, then what the home earns a year, mortgage and all, if you later rent it out, sell it, or keep it for good, next to your investments. It uses your tax picture from step 1 and your expected return from step 2.

The home
Owning and renting

Property tax and maintenance are a share of the home's value; maintenance of about 1% a year is a common rule of thumb. Realtor commissions are negotiable: set 0% to sell without one, or about 5% to 6% if you pay both the listing and the buyer's agent. Other selling costs cover transfer taxes, attorney and title fees. The typical costs are rough regional averages: adjust them to the actual home.

Later: rent it out, keep it as a second home, or sell

Live in a home 2 of the 5 years before selling and up to $250,000 of gain ($500,000 married) is tax-free, so you have 3 years after moving out to sell. Rental property is depreciated over 27.5 years on the building's value (not the land); that depreciation is taxed when you sell. A second home earns no rent, but you can count what using it is worth to you, like the vacation rentals you'd otherwise pay for. Set "Live in it for" to 0 for a home you buy only as a second home or a rental.

Rent or buy: your net worth

If you sold after each year, after selling costs and taxes. Whoever spends less each year invests the difference at your expected return.

What the home earns a year

Your down payment and closing costs, every year's costs and income (counting the rent you don't pay while you live there), and what you'd net at the end, as one annualized return after tax, next to your investments over the same years.

3The long game

Your plan from steps 1 and 2, at your return and at 4% to 10% for comparison. Small differences in return compound into big differences over time.

Also: should you pay down debt or invest?

You have some extra money each month. Put it toward the debt first, or invest it while paying only the minimum? Either way, once the debt is gone, the whole payment gets invested.

Compound Slowly is a free educational tool from Memento Financial Planning, a fee-only fiduciary firm. For illustration only, not financial or tax advice. Returns are never guaranteed. See all assumptions.