Methodology

Converting between frequencies

Each frequency is converted to a fixed number of payments per year: daily 365, weekly 52, fortnightly 26, monthly 12, quarterly 4 and yearly 1. Your amount is multiplied by that count to reach an annual figure.

Leap years

A year is always treated as 365 days. Leap days are deliberately excluded so results stay stable and reproducible; including them would change a 30-year daily total by roughly 0.2%.

Applying annual increases

The expense amount increases at the start of each new year and compounds on the previous year's amount, not the original amount. The first year always uses the amount you entered.

Investment growth

Contributions are assumed to occur at the end of each payment period — an ordinary annuity. The annual return you choose is converted to an equivalent per-period rate so that daily, monthly and yearly frequencies compound consistently.

Worked example: $100 a month for 10 years at 6% gives i = 1.06^(1/12) − 1 ≈ 0.004868, n = 120, and a future value of approximately $16,247.

What each result means

• Total spent — money actually paid out, in nominal dollars.
• Future investment value — contributions plus projected growth if the same payments had been invested instead.
• Investment earnings — the growth only: future value minus contributions.
• Total opportunity cost — the full future investment value, because both the money and its potential growth are forgone. We never label growth alone as the opportunity cost.

Inflation and today's money

Nominal values are the raw dollar amounts. Today's-money values divide future amounts by (1 + inflation) raised to the number of years, so you can judge purchasing power rather than headline size.

Rounding

Calculations run at full floating-point precision and rounding happens only at display time — to whole dollars for large figures and to cents for daily amounts. Chart values are rounded to whole dollars.

Why projections are illustrative

Real returns vary year to year, and fees, taxes and behaviour all affect outcomes. A single assumed rate is a useful comparison tool, not a forecast. See the disclaimer.