A return is mostly arithmetic about paper you already have. Five minutes here and the arithmetic makes sense — then, right after this page, every line a receipt can support, with what its paper must show.
Income, then deductions, then credits
Start with what the CRA already knows. Your income arrives on slips, and it is mostly spoken for — tax came off each paycheque before you ever saw it. The return's first job is simply to add that income up.
What happens next is the part you control. Deductions come first: they shrink the income being taxed. Credits come last: they shrink the tax itself. The book before this one covered why the difference matters. This one is about the order, because the order explains something odd: the same receipt can be worth different amounts to different people. A deduction saves tax at your highest rate, so it saves more for a higher earner. Most credits are worked out at one low rate for everyone, so they treat every filer about the same. Either way, the rule holds: a deduction shrinks your income, a credit shrinks your tax, and both run on paper.
The slips that start it
A T4 is your employer telling the CRA what it paid you and what it held back. A T5 is your bank doing the same for the interest your savings earned. The CRA gets its own copy of every slip before you file. So you never claim a slip — it is already claimed. You keep it anyway, because it anchors everything else: the return you send in has to match the slips the CRA is holding. When you capture a slip, Dossier identifies it, labels it by year and type, and files it beside your receipts, so the whole year's paper lives in one place.
Every line has its own demands
The lines you claim against run on receipts — but not just any receipt. Each line asks the paper to prove specific things. A daycare receipt needs the provider's SIN on it. A donation receipt needs the charity's registration number. A slip of thermal paper that says only APPROVED proves you paid somebody something, which is not a tax position.
That is why every claimable line in this Guide has its own page, carrying the checklist for that line's paper, sourced from the CRA. When you capture a document, Dossier reads it and holds the reading up against the checklist. Anything missing becomes a question, not a rejection — a daycare receipt with no SIN is kept and flagged, and the gap travels with the document until you settle it.
Lines that run on a certificate
A few lines have no receipts behind them at all. The disability tax credit is the clearest case: it runs on Form T2201, certified by a medical practitioner and sent to the CRA, and it applies only once the CRA has approved it. No shoebox of receipts unlocks a line like this — the paper is one certified form, not a year of collecting. The line pages marked with the certificate sign explain each of these claims: what the form is, who certifies it, and what happens after.
When a line stops existing
Credits come and go with federal budgets. The federal education and textbook amounts, for example, were ended for new tax years — students went on claiming tuition, but those two lines stopped existing going forward. Retired lines still matter, though. A past-year return follows the rules of its own year, so an old receipt can still support a line that no longer exists today. The Guide keeps retired lines on the list, marked as retired, for exactly that reader: someone assembling an earlier year, holding paper that was claimable when it was printed.