Two calculators price the same instinct, a client paying more than the mortgage requires, in two different ways. Open Tools > Calculators and pick the one that matches what the client actually has: a lump sum or a bigger payment, or a linked deposit account.
The Prepayment Calculator
Attach a deal or enter the mortgage balance, rate, and amortization directly, then add a one-time lump sum, extra dollars per month, or both. The calculator applies every dollar straight to principal, which is what shortens the term. Leave a field blank and it drops out of the comparison rather than defaulting to a guess.
A Lump Sum Against Extra Every Month
The two prepayment fields work together, not as alternatives. A client putting a bonus against the mortgage and raising their monthly payment gets both effects priced in one pass, against the same starting balance and rate. The monthly payment shown is the base payment plus whatever extra the client commits to, so the tile never understates what actually leaves their account.
The Offset Calculator
An offset account is not a prepayment. It is a deposit account linked to the mortgage, and the balance never touches principal directly. Enter the average balance the client expects to keep linked, and the calculator charges interest only on the mortgage balance above it, the interest-bearing balance. The payment itself is held at what a mortgage with no linked account would charge, so the interest the client no longer pays goes straight to principal instead, and the term shortens the same way a prepayment would. This is the mechanic behind readvanceable products such as Manulife One.
Reading Interest and Time Saved
Both calculators lead with the same two figures, interest saved and time saved, next to the payoff date and total interest with and without the change. On the offset side, treat the number as a best case: the comparison assumes the linked balance stays where the client says it will, on average, and a chequing balance that dips partway through the month raises the interest actually charged. Say that out loud before a client anchors on the headline figure.
Checking the Client's Prepayment Privileges First
Prepayment privileges, the annual lump sum percentage and the payment increase percentage, are set by the lender and the product, and they are usually capped. The calculator has no way to know what a specific mortgage allows; it prices whatever lump sum or extra payment is typed in, penalty-free or not. Before presenting a result, check the client's actual privileges on the mortgage or the commitment letter, so the number reflects what they can prepay without triggering a penalty, not just what fits in the input field.
What to Do Next
Use Explain a Mortgage to a Client to walk through where an ordinary payment goes before showing what paying extra changes.