The Rates tab holds the MRI rate and the income thresholds, each editable and dated — because tax rates change by law, you confirm the current figure on KRA iTax and, if it's moved, edit one cell. On the Rent tab you log the rent received each month per property; the tax due computes on the gross automatically.
The Dashboard totals your gross rent and the MRI due, shows your effective rate, and checks whether your annual rent falls inside the MRI band — below the lower threshold or above the upper one, different rules apply, and it tells you so rather than quietly giving a wrong number. The formulas are locked; only the yellow cells accept typing.
MRI is an operational tax on gross rent; to keep the underlying records — units, tenants, arrears and receipts — use the free Rental Income & Tenant Tracker alongside it.