Bridging Interest Calculator: Rolled-Up vs Retained Interest Explained
When you take out a bridging loan, the lender doesn't always collect interest monthly. Instead, UK bridging lenders typically structure interest in one of two ways: rolled up or retained. Understanding which method your loan uses — and how to calculate the total cost under each — is essential before you commit.
This guide explains both methods with worked examples, shows you how to calculate your own numbers, and covers which option is better in different scenarios.
How Bridging Interest Works
Unlike a residential mortgage, a bridging loan doesn't require you to make monthly interest payments in most cases. The interest is charged on the outstanding balance each month and either:
- Added to the loan (rolled up) — you pay nothing during the term; the interest accumulates and you repay everything at the end
- Deducted upfront from the loan (retained) — the lender sets aside the full interest amount on day one, reducing the net funds you receive
Both methods mean you receive less than the gross loan amount, or owe more than you borrowed. The mechanics and total cost differ.
Rolled-Up Interest: How It Works
With rolled-up interest, the lender adds the monthly interest charge to your outstanding loan balance each month. You pay nothing during the term. At redemption, you repay the original loan plus all accumulated interest.
Example: Rolled-Up Interest
Loan details:
- Gross loan: £400,000
- Interest rate: 0.85% per month
- Term: 9 months
Monthly calculation:
| Month | Opening Balance | Interest (0.85%) | Closing Balance |
|---|---|---|---|
| 1 | £400,000 | £3,400 | £403,400 |
| 2 | £403,400 | £3,429 | £406,829 |
| 3 | £406,829 | £3,458 | £410,287 |
| 4 | £410,287 | £3,487 | £413,774 |
| 5 | £413,774 | £3,517 | £417,291 |
| 6 | £417,291 | £3,547 | £420,838 |
| 7 | £420,838 | £3,577 | £424,415 |
| 8 | £424,415 | £3,608 | £428,023 |
| 9 | £428,023 | £3,638 | £431,661 |
Total interest paid: £31,661 Redemption amount: £431,661
Note that rolled-up interest compounds — you're paying interest on interest each month. This is why the interest amount increases slightly each month even though the rate stays the same.
Net Funds Received (Rolled-Up)
With rolled-up interest, you receive the full gross loan amount on day one (less fees). You don't give anything back — instead, you owe more at the end.
Gross loan: £400,000 Less arrangement fee (1.5%): -£6,000 Less broker fee (1%): -£4,000 Net funds received: £390,000
Retained Interest: How It Works
With retained interest, the lender calculates the total estimated interest for the full term and deducts it from the loan upfront. You receive the net funds immediately. If you repay early, the unused retained interest is returned to you.
Example: Retained Interest
Same loan details:
- Gross loan: £400,000
- Interest rate: 0.85% per month
- Term: 9 months
Retained interest calculation:
Unlike rolled-up, retained interest is calculated as a simple (non-compounding) figure on the gross loan:
Retained interest = £400,000 × 0.85% × 9 months = £30,600
Net funds received: £400,000 − £30,600 = £369,400 (further reduced by fees)
The lender holds the £30,600 in reserve. You repay the gross loan (£400,000) at the end, not more — so the redemption amount is simpler.
Net Funds Received (Retained)
Gross loan: £400,000 Less arrangement fee (1.5%): -£6,000 Less broker fee (1%): -£4,000 Less retained interest: -£30,600 Net funds received: £359,400
Rolled-Up vs Retained: Which Is Cheaper?
| Metric | Rolled-Up | Retained |
|---|---|---|
| Net funds received | £390,000 | £359,400 |
| Total interest cost | £31,661 | £30,600 |
| Redemption amount | £431,661 | £400,000 |
| Effective difference | Pay more at end | Receive less upfront |
Total interest: retained is slightly cheaper (£30,600 vs £31,661) because it's calculated as simple interest on the gross loan, while rolled-up compounds monthly. The difference grows with the term length.
However, retained reduces your net funds significantly. On a £400,000 loan over 9 months, you receive £30,600 less upfront with retained vs rolled-up. If you need the full loan amount available for your project, rolled-up is the better structure — you access all the money immediately.
Early Repayment and Retained Interest
One important advantage of retained interest: if you repay early, you get the unused interest back.
In the example above, if you repay at month 6 instead of month 9:
- Used interest: £400,000 × 0.85% × 6 = £20,400
- Unused interest returned: £30,600 − £20,400 = £10,200
With rolled-up interest, there's no unused interest to return — you simply owe the accumulated balance at redemption (which is lower than if you'd gone to the full term, but there's no "refund").
If you're confident you'll repay early, retained interest can be cheaper overall. If you might use the full term, rolled-up often works out similarly — and leaves more cash in your hands upfront.
How to Calculate Your Own Bridging Loan Cost
Use these steps to calculate the total cost of any bridging loan:
Step 1: Calculate Monthly Interest
Monthly interest = Loan amount × Monthly rate
Example: £500,000 × 0.90% = £4,500/month
Step 2: Calculate Total Interest
For rolled-up: use the compounding formula or calculate month by month as in the table above.
Approximate total (compounding): Gross loan × ((1 + monthly rate)^term − 1)
£500,000 × ((1.009)^12 − 1) = £500,000 × 0.1135 = £56,750 total interest
For retained: simple multiplication.
£500,000 × 0.90% × 12 = £54,000 total interest
Step 3: Add All Fees
| Cost | Amount |
|---|---|
| Arrangement fee (1.5%) | £7,500 |
| Exit fee (0.5%) | £2,500 |
| Broker fee (1%) | £5,000 |
| Legal fees (yours + lender's) | £4,000 |
| Valuation | £800 |
| Total fees | £19,800 |
Step 4: Total Cost of Funds
Total interest + Total fees = £56,750 + £19,800 = £76,550 (for rolled-up, 12-month term)
As a percentage of the loan: £76,550 / £500,000 = 15.3% total cost of funds
Common Questions
What's the minimum I need in my account to service a bridging loan? For rolled-up and retained interest structures, you don't make monthly payments. You need to be able to repay the full redemption amount from your exit (sale proceeds, refinance funds, etc.). No monthly cash reserves needed for the interest.
Can I switch from retained to rolled-up mid-term? No — the interest structure is fixed at drawdown. Make sure you've chosen the right structure before the loan completes.
Does the interest rate change during the term? Most bridging loans have a fixed monthly rate for the term. Some lenders allow rate reductions if you hit certain milestones (e.g., planning granted, works completed). Penalty rates apply if you exceed the term — see our guide on what to do if you miss your exit deadline.
Do development finance drawdowns affect the interest calculation? Yes — development finance is drawn in stages (tranches), so interest is calculated on the outstanding balance after each drawdown, not the total facility from day one. This is one of the key differences between bridging and development finance.
Are bridging loan interest rates annual or monthly? Always check. Lenders quote monthly rates (0.85%/month) but sometimes also express these as annual equivalents. Monthly 0.85% is approximately 10.7% per year (simple) or 10.68% AER — but when fees are included, the true annual cost is significantly higher as shown in the examples above.
Getting an Accurate Quote
The calculations above give you the framework, but the exact cost depends on your specific loan terms, lender, and fees. The best way to compare is to ask lenders (or your broker) for a full cost illustration showing:
- Gross loan amount
- Interest method (rolled-up or retained)
- Total interest
- All fees itemised
- Net funds received
- Redemption amount
At The Finance Brokers, we provide a full cost breakdown for every loan we source — including all fees from every party, not just the headline rate. Get in touch for a comparison across the market.