How Loan APR Is Calculated: Per-Day Rates, Fees and GST, With Worked Examples

"Sirf 0.1% per day." "Processing fee only 2%." "Interest just ₹354!" — every one of these statements can be true while the loan quietly prices at 80% a year. The device that exposes this is the APR — Annual Percentage Rate — the single number the RBI forces onto every digital loan's Key Fact Statement precisely because it cannot be gamed by splitting cost into small-sounding pieces. Learn to compute it once and you become immune to the entire genre of per-day-rate marketing.

What APR is, in one sentence

APR is the total cost of the loan — interest plus all fees — expressed as an annualised percentage of the money you actually received. Three design choices give it teeth:

1. All-inclusive. Processing fee, documentation charges, mandatory insurance, GST on those fees — everything the loan costs you goes into the numerator. Interest-only "sticker rates" ignore the fee stack; on short tenors the fee stack is often most of the cost.
2. Computed on net disbursed money. Fees are usually deducted upfront, so you received less than you're paying interest on. APR uses what hit your bank account.
3. Annualised. Cost is scaled to a full year, making a 21-day loan comparable with a 3-year loan on one axis. (Formally, KFS APR is computed as an internal rate of return on the actual cash flows; for single-bullet short loans the simple formula below lands within a whisker of it.)

The working formula for bullet-repayment loans:

APR ≈ (Total cost of credit ÷ Net disbursed amount) ÷ Tenor in days × 365 × 100

The ingredients, and where they hide

Worked example 1: ₹10,000 for 30 days — the "0.1% per day" loan

Terms: ₹10,000 sanctioned, 30 days, 0.1% per day interest, 3% processing fee, single bullet repayment.

Now the honest annualisation:

APR = (654 ÷ 9,646) ÷ 30 × 365 × 100 ≈ 82%

Read that against the marketing. "0.1% a day" sounds like 36.5% — already steep — but the fee stack on a 30-day tenor more than doubles it. Notice the mechanism: the ₹354 of fees would be trivial spread over 3 years, but you're paying it for 30 days of money. Short tenor is a fee amplifier. The same loan taken for 15 days would price near 120% APR with identical "small" fees.

Total cost check, always: you received ₹9,646 and will repay ₹10,300 — the loan costs ₹654, about 6.8% of your money in one month. That's the number to say out loud before accepting.

Worked example 2: ₹50,000 for 6 months — the EMI loan

Terms: ₹50,000 sanctioned, 6 monthly EMIs, sticker rate 24% p.a. on reducing balance, 2% processing fee.

Step 1 — EMI. At 2% per month reducing over 6 months, EMI = ₹8,926 (any EMI calculator confirms). Total repaid: ₹53,559 → interest component ₹3,559.

Step 2 — the fee stack. PF ₹1,000 + GST ₹180 = ₹1,180, deducted upfront. Net disbursed: ₹48,820.

Step 3 — total cost of credit. ₹53,559 repaid − ₹48,820 received = ₹4,739.

Step 4 — annualise honestly. With instalment loans, the simple bullet formula misleads (your average outstanding is roughly half the principal), so APR is found as the IRR of the cash flows: +₹48,820 in, −₹8,926 × 6 out monthly. That solves to about 2.72% per month, i.e. an APR of roughly 33%.

Sticker said 24%. Truth: ~33%. The 2% fee "cost" nine percentage points of APR — and again, the shorter the tenor, the worse this gets. The same fee on a 3-year loan would add barely 1.5 points.

The two examples, side by side

This table also teaches APR's one limitation: APR measures rate, not rupees. The 30-day loan has a horrifying APR but costs ₹654; the 6-month loan has a moderate APR but costs ₹4,739. Use APR to compare competing offers for the same need; use total cost of credit to decide whether the need justifies borrowing at all. Any instalment figure you're quoted should always sit next to its total: "₹8,926 × 6" means "₹53,559 on ₹48,820 received".

Marketing tricks the APR lens defeats

• Per-day framing. "0.1% daily" reads as one-tenth of one percent; it is 36.5% annually before fees. Multiply by 365, always.
• Flat-rate quoting. "12% flat" on an EMI loan charges interest on the original principal all tenor long, though you're repaying monthly — a 12% flat rate is roughly a 21–22% reducing rate. The APR computation sees through it automatically because it only looks at actual cash flows.
• Fee splitting. ₹99 platform fee + ₹149 documentation + 1.5% PF + GST — four small numbers instead of one honest one. The APR sums them.
• "Low EMI" stretching. Halving the EMI by doubling the tenor raises the total interest you pay. The instalment fell; the cost rose.

Mental anchors worth memorising

A few conversions, carried in your head, defeat most pricing theatre on the spot:

The last two rows are the ones lenders least want internalised: a fee's APR impact is inversely proportional to tenor. Any fixed fee on a very short loan dominates the pricing.

Your verification ritual

1. From the KFS: net disbursed amount, total of all repayments, tenor.
2. Total cost = total repayments − net disbursed.
3. Bullet loan → apply the formula above. EMI loan → use an APR calculator (IRR-based) rather than hand math.
4. Compare against the KFS's printed APR line. Small gaps (rounding, date conventions) are normal; a gap of many points means a charge is hiding outside the KFS — which the rules don't permit, and which you should query with the lender's grievance officer before signing.

Thirty seconds of arithmetic is the entire defence. Rate ka jhooth pakadna easy hai — bas har cheez ko saal ka banao, aur mile hue paise se divide karo.