Return Ledger

Time-weighted return (TWR): the ledger is split into sub-periods at each row where a value is actually known (a valuation row, or a deposit/withdrawal you also priced). Between two known values, Modified Dietz estimates the sub-period return from the start value, end value, and the dated flows in between, weighted by how long each was invested — no value is required at every single flow. The sub-period returns are chain-linked, then annualized over the full span. With only an opening and a closing value, this collapses to one Modified Dietz estimate for the whole period.

Money-weighted return (XIRR): every deposit and withdrawal is treated as a signed cash flow on its date, with the final value as a closing inflow; the annual rate that makes their net present value zero is found numerically (Newton‑Raphson with a bisection fallback). XIRR never needs interim values — only dated flows and the current value. If the first row is a valuation carrying a pre-existing balance rather than a deposit, that balance is treated as if it were invested on that date, since XIRR has no way to know when it actually went in — skipping it would understate the invested capital and wildly overstate the return.

Fees, tax, and gross vs. net: the Amount field always stays the gross figure — what actually moved in or out of the account, matching your broker statement. That's what TWR uses, so it keeps measuring market performance on its own, undistorted by what you paid in costs. Fees and tax you log on a Deposit or Withdraw only feed a second, separate figure: XIRR · net, computed on the amount minus fees and tax (what actually reached your pocket, or cost you extra on the way in). The gap between gross and net XIRR is the cost drag tile — roughly how many percentage points a year fees and tax are costing you. Tax withheld on unrealized gains inside valuation checkpoints isn't captured this way; only tax you actually record against a withdrawal is.