Plans guide

What is Plans?

Plans is a simulation sandbox. Nothing here touches your real transactions, accounts, or budgets. You can model life events to see how they play out month by month before you commit to anything.

There are four templates:

• Trip. Model a single trip's cost on a start date (transport plus accommodation per night plus a daily budget multiplied by duration). The cost lands in one dip; the rest of the horizon is just your regular cashflow.
• Purchase. Model a one-off purchase (car, house deposit, appliance). The down payment lands on the target date.
• Retirement. Model long-horizon savings. Compound interest, monthly contributions, optional step-function contribution curve, and an inflation- adjusted real-terms overlay on the chart.
• Custom. A fully editable plan type for anything that doesn't fit the three templates above. You add a list of events to the timeline and the simulator replays them month by month. Five event types are available:
  • income_off: silence your recurring income for a date range (sabbatical, parental leave, a planned career break).
  • expense_off: silence recurring expenses for a date range, optionally scoped to a single category (cancel the gym while travelling).
  • recurring_on: marker for the future exclude-recurring base flag. Currently a documented no-op; the event lands on the plan but the simulator does not yet alter the baseline.
  • one_off_income: a single income lump on a given month (bonus, tax refund, gift).
  • one_off_expense: a single expense lump on a given month (replacement laptop, vet bill).
  Example: plan a 3-month sabbatical by adding anincome_off from month 6 to month 9 and watch the chart show the dip and the recovery once income resumes.

The verdict colors

Every simulated plan gets a verdict: green, yellow, or red. The verdict reads what the chart shows.

• Green. Your accounts stay healthy and the plan's end balance is at least 80 percent of where it started (or, for retirement, at least the target).
• Yellow. Either you'll briefly dip below zero on an account, or the plan eats more than 20 percent of your starting net worth. Doable, but not comfortable.
• Red. The plan causes an extended cash crunch, or (for retirement) you'll fall more than 15 percent short of your target. Tune the params and re-simulate.

Below the verdict, the projection panel lists alerts (any month an account dips below zero) and suggestions ("raise monthly contribution by 200 to close the gap"). Suggestions are advisory, never automatic; the plan only changes when you change the params.

How the math works

Trip and Purchase

We project month by month. We start with your account balances as of today, apply your recurring income and expenses plus current budget pace, and drop in the plan's cashflow events on their scheduled months. For a trip, that's a single dip on the start month equal to transport plus (accommodation per night times duration) plus (daily budget times duration). For a purchase, it's the down payment on the target date.

Retirement

Retirement uses compound interest, applied monthly. Each month the balance grows by your annual return divided by 12, and your monthly contribution is added on top.

We also track the same balance in real (inflation- adjusted) terms so the chart's red dashed line tells you what your future money would be worth in today's pounds, euros, or dollars. The formula:

real_balance = nominal_balance / ((1 + inflation_rate) ^ years)

Both annual return and annual inflation are expressed as percentages and converted to monthly factors internally. Common assumptions for long-term diversified stock portfolios range from 5 to 8 percent annually; check your own risk tolerance and historical returns for your asset mix. The European Central Bank targets 2 percent annual inflation; actual long-run averages vary by decade and by country, so use a value that matches your assumptions for the period you are projecting. Your own assumptions are what matters.

Smooth with regression

When the engine sees enough recent history, it can fit a straight line through your last 12 months of cashflow and use the trend instead of the raw recurring numbers. This is helpful when your income has been growing or your spending has shifted, and you don't want a one-off month skewing the projection. The projection panel shows a "Trend-adjusted" badge when this kicks in.

How to use Plans

1. Click + New plan and pick a template.
2. Fill in the params. The chart re-simulates as you type (about 400 ms after you stop). Inline validation errors (a curve row missing its start date, for example) skip the re-simulate until you fix them.
3. Read the verdict and the suggestions below the chart.
4. Tweak params (raise the monthly contribution, push the retirement date out, lower the trip's daily budget) and watch the chart respond.
5. The editor auto-saves as you type (about 400 ms after you stop). Your plan stays in your list under/plans, ready to revisit and edit later. Use the Re-simulate button if you want to refresh the chart with your latest changes without waiting for the debounce.
6. When you have two or more plans, the Compare plans surface lets you put up to three side by side on the same chart.

The right pane shows the projection; the left pane is the editor. The two stay in sync on every keystroke. Use the Re-simulate button if you want to force a fresh run after switching accounts or after a recurring template change.

The contribution curve (step function)

Most people don't save a flat amount across 30 years. Maybe you save 500 a month now but plan to bump to 1,000 a month once your mortgage is paid off, then 1,500 a month when the kids leave school. The contribution curve is how you model that.

Each row in the curve table sets a new monthly contribution starting on a given date. Rows must be in chronological order. The base contribution applies before the first row's date.

Worked example

Current age 30, retirement at 65, base monthly contribution 500. Add curve rows:

• From age 40 (year + 10): 800 per month.
• From age 50 (year + 20): 1,200 per month.

The projection then runs:

• From age 30 to age 40: 500 per month (base).
• From age 40 to age 50: 800 per month.
• From age 50 to age 65: 1,200 per month.

If you fill in a curve row's amount but not its date, the form shows an inline validation error and the auto re- simulate pauses until you fix it. The error is intentional; it stops a half-typed row from getting saved against your plan.