Loanable Funds Market graph mistakes

15 ways students lose points on this diagram, each taken from a worked free-response scenario. Every entry names the reasoning that causes the error, not just the error, because the wrong answer is usually a sensible thought applied to the wrong curve.

1. 01

   Financing the Deficit

   The mistake. Many students shift the supply of loanable funds left instead, reasoning that government borrowing takes funds away from private borrowers. The government here is a borrower, not a lender, so its new bonds add to the borrowing side; the crowding out of private investment shows up as the higher interest rate reducing the quantity of funds firms borrow along their own unchanged demand schedule, not as a leftward shift of supply.

   Draw this instead. Demand for loanable funds shifts right.

   Exam tip. Decide first whether the government is raising money or returning it. Issuing new bonds puts the government on the borrowing side of the graph, and running a surplus to retire debt puts it on the lending side.

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2. 02

   Household Saving Behavior

   The mistake. A frequent wrong answer is to shift the demand for loanable funds right because households are spending more, importing the logic of the product market where extra consumption raises demand. The demand curve here is borrowing to finance capital, and the stem holds firms' investment fixed; what actually changed is how much income households release to lenders.

   Draw this instead. Supply of loanable funds shifts left.

   Exam tip. Find the sentence about saving out of income. Whatever happens to that flow happens to the supply of loanable funds, no matter which motive the stem gives for the change.

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3. 03

   Investment Tax Credit

   The mistake. The classic wrong answer is to shift demand left, reasoning that if the credit makes each machine cheaper then firms need to borrow fewer dollars to buy the equipment they already planned on. A credit raises the after-tax return on capital, so projects that were not worth financing before now clear the hurdle; firms buy more equipment rather than buying the same equipment for less, and total borrowing rises.

   Draw this instead. Demand for loanable funds shifts right.

   Exam tip. Memorize the three things that move the borrowing side of this graph: expected profitability, the productivity of new capital, and taxes that hit the return on capital. An investment tax credit is the second-most-tested of them after government borrowing, and it always moves demand right.

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4. 04

   Wave of Business Optimism

   The mistake. Some students shift supply right, treating confident and soon-to-be-profitable firms as having more money to lend out. Firms sit on the borrowing side of this model; expected future sales change how much financing they want, not the pool of household saving available to lend.

   Draw this instead. Demand for loanable funds shifts right.

   Exam tip. Expectations about future profitability are a determinant of investment demand. When the story is about what firms plan to build, move the demand curve and say in words that saving is unchanged, because rubrics award the second point for that.

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5. 05

   Retiring National Debt

   The mistake. The usual competing answer is to shift demand left on the grounds that the government is borrowing less. That treatment fits a government that cancels planned new bond issues, but this stem has the government handing cash back to bondholders out of a surplus, which is public saving entering the lending side of the market.

   Draw this instead. Supply of loanable funds shifts right.

   Exam tip. Name the result, not just the shift. When the government adds to national saving the real interest rate falls and firms borrow more along an unchanged demand curve, which is crowding in, and free-response rubrics regularly award a point for using that term correctly.

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6. 06

   Foreign Capital Inflow

   The mistake. Students frequently shift demand right because foreign investors are buying Dorian assets, and buying sounds like demanding. In this market, buying a bond is lending, so the foreign investors join the supply side; the demanders are the firms and the government issuing those bonds.

   Draw this instead. Supply of loanable funds shifts right.

   Exam tip. Translate every financial story into lender or borrower before you draw anything. Bond buyers supply loanable funds and bond issuers demand them, whatever the nationality of either side.

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7. 07

   Idle Factory Capacity

   The mistake. Many students shift supply right because idle capacity sounds like spare resources piling up and waiting to be used. Unused machines are physical capital, not lendable funds, and nothing in the stem changed how much income households make available to lenders; what changed is how many projects firms want to finance.

   Draw this instead. Demand for loanable funds shifts left.

   Exam tip. Ask what the story does to the number of profitable capital projects. When firms already own all the capacity they need, their borrowing schedule moves left even though not one word of the stem is about saving.

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8. 08

   Robotics Productivity Leap

   The mistake. A common wrong answer is to shift supply right, treating a technological leap as making the whole country richer and therefore better able to save. The stem fixes household saving at each real interest rate, and new technology reaches this graph through the return firms expect on new equipment, which is a decision about how much to borrow.

   Draw this instead. Demand for loanable funds shifts right.

   Exam tip. Draw the shift, then say what the interest rate does to the other side. Here the higher rate pulls savers up along an unchanged supply curve, and calling that a movement along rather than a shift is often worth its own rubric point.

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9. 09

   An Aging Population

   The mistake. Students often shift demand left instead, reasoning that an older, smaller workforce means the economy produces and spends less, so firms need less financing. The stem holds firms' desired investment fixed at each interest rate, and retirees drawing down wealth changes who is lending, not who is borrowing.

   Draw this instead. Supply of loanable funds shifts left.

   Exam tip. Demographics reach this graph through saving. Ask whether the group described is adding to the pool of funds or drawing it down, then move the lending side and leave borrowing alone.

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10. 10

    Tax Break for Savers

    The mistake. The most common error is to draw no shift at all and simply slide up the existing supply curve, on the grounds that savers are now earning more. The rate on the vertical axis has not changed; the policy changes how much households save at each of those rates, and a change at every rate is a shift of the whole curve.

    Draw this instead. Supply of loanable funds shifts right.

    Exam tip. Only a change in the variable on the vertical axis produces a movement along a curve. A tax that changes what savers keep at every one of those rates shifts the curve, and on this graph an answer that moves nothing is scored as wrong.

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11. 11

    Savings Head Overseas

    The mistake. Students often shift demand right, reasoning that the overseas construction boom needs financing and therefore adds borrowers to the picture. The graph is Brenmark's own market, and the foreign builders borrow in their own market, not this one; what leaves Brenmark is lendable funds, which belongs on the saving side.

    Draw this instead. Supply of loanable funds shifts left.

    Exam tip. Identify whose market the graph shows before you move anything. Funds crossing a border cut the lending side in the country they leave at the same time as they add to it in the country they enter.

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12. 12

    Corporate Profits Tax Hike

    The mistake. Many students shift supply right, reasoning that the government now collects more revenue and therefore saves more. The stem holds the budget balance fixed because the extra revenue is fully spent, so no public saving is created; the tax bites on the return to new capital, which is exactly what firms borrow to finance.

    Draw this instead. Demand for loanable funds shifts left.

    Exam tip. Ask whose return the tax bites before you draw. A tax on the return to new capital moves the borrowing side, a tax on the return to saving moves the lending side, and the two shift opposite curves in opposite directions.

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13. 13

    Deficit Meets Retirement Wave

    The mistake. The dominant wrong answer is to report both outcomes as determinate, almost always as "the real interest rate rises and the quantity of loanable funds rises," because government borrowing is the headline event and students carry over the answer from the single-shift deficit question. Only the interest rate has a determinate direction here. Demand shifting right raises the quantity and supply shifting left lowers it, and the stem gives no information about the relative sizes, so any signed claim about quantity is unsupported. The other common failure is to draw only the deficit and leave the saving side untouched, which turns a two-shift question into a one-shift answer and gives up the second shift point outright.

    Draw this instead. Demand for loanable funds shifts right and Supply of loanable funds shifts left.

    Exam tip. Check each axis on its own before you write a word: name a direction only where the two shifts push the same way, and where they conflict write the word indeterminate and say what it depends on, because rubrics award that point for the explicit statement and never for a hedge.

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14. 14

    Export Boom and Safe Haven

    The mistake. Students overwhelmingly claim both outcomes are determinate, and the usual pair is "the quantity rises and the real interest rate rises," because the investment story looks like the tax credit and business optimism questions where the rate always went up. Here the foreign inflow pushes the rate the other way, and with no statement about which shift is larger the rate has no determinate sign. A second error is to put the foreign savers on the borrowing side because they are buying Torvanese bonds: buying a bond is lending, so those funds join the saving side of the market.

    Draw this instead. Demand for loanable funds shifts right and Supply of loanable funds shifts right.

    Exam tip. Learn the pattern by axis: when both curves shift the same way the quantity is settled and the interest rate is not, and when they shift opposite ways the interest rate is settled and the quantity is not, so state the determinate result first and then name the indeterminate variable with the comparison it turns on.

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15. 15

    Idle Plants, Forced Saving

    The mistake. The characteristic error is treating both outcomes as determinate, typically as "the real interest rate falls and the quantity of loanable funds rises," on the reasoning that cheaper borrowing must mean more lending happens. Only the rate is determinate. Demand shifting left cuts the quantity and supply shifting right raises it, and the stem never ranks the two, so the quantity has no sign. Students also frequently mistake the idle machinery for spare funds and shift the saving side for it: unused equipment is physical capital, and what it actually changes is how many projects firms want to finance.

    Draw this instead. Demand for loanable funds shifts left and Supply of loanable funds shifts right.

    Exam tip. Draw both shifts on the graph before you commit to any conclusion, because reading the new equilibrium off a picture with two curves moved is the only reliable way to see which axis is pinned down and which one can go either way depending on the relative size of the shifts.

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