T-bills Calculator and Purchase Tracking Sheet

Karatasi T-Bill Tracker

The complete Excel workbook for managing a Kenyan Treasury bill portfolio. Calculate your real net earnings after withholding tax and bank custody fees, compare 91, 182 and 364 day tenors, and track every purchase across the year in a clean register.

Why most T-bill calculators get this wrong

The headline auction yield is gross. It is not what lands in your account. Two things get deducted before you see a shilling. Withholding tax takes 15% of your interest and Bank custody fees. By the time the money settles, your effective net yield can be a full percentage point below the rate that drew you to the auction.

This workbook makes both visible, side by side, every time.

What's inside

Seven sheets, designed to be used in order or jumped into directly.

• Start Here. A plain language welcome, the four step journey, and a worked example using realistic Kenyan numbers.
• Step 1. Your Goals. Enter your capital and target net annual return. A live feasibility check tells you whether the target is realistic at current CBK auction rates.
• Step 2. T-bill Basics. A side by side comparison of the three tenors, how the discount mechanic works, and exactly what withholding tax and bank custody fees do to your earnings.
• Step 3. Calculator. Enter face value, tenor, yield, withholding tax and bank fees. The right panel breaks down discount, purchase price, tax deducted, fees deducted, net interest, and effective net annual yield. Compares automatically against your target from Step 1.
• Step 4. Compare Tenors. Same capital across 91, 182 and 364 day options. Shows the net interest from one term and the annualised earnings if you roll. The winner is highlighted automatically.
• Step 5. Track Purchases. A 20-row register for actual T-bill buys. Enter purchase date, tenor, face value, yield and fees. Maturity dates, prices, deductions and net interest fill themselves in.
• Summary. Plan vs actual dashboard. Capital deployed, gross interest, net interest, effective yield, gap to target. Updates as you log each purchase.

Built around Kenyan reality

• KES 100,000 minimum, in multiples of KES 50,000
• 91, 182 and 364 day tenors as the CBK actually issues them
• Withholding tax as a variable, defaulting to 15%, with notes on exemption rules
• Bank custody fees as a percentage prorated for the tenor, plus an optional flat transaction fee
• Direct DhowCSD route clearly noted as the way to avoid custody fees entirely
• References throughout to where current auction rates and prospectuses live on the CBK site

Who it's for

Individual investors who already understand the basics of T-bills and want a clean place to plan and record what they buy. Particularly useful if you are running a T-bill ladder (rolling 91 day bills monthly), comparing CBK auctions against money market funds, or planning your year's fixed income allocation against a specific income target.

Who it isn't for

If you have never bought a T-bill before, start with our free T-Bill Calculator on the tools page. It runs single scenarios with no commitment. This tracker assumes you are ready to build and manage a real portfolio.

Honest framing

This is a planning and tracking tool, not a forecast. Auction yields move every Wednesday. Withholding tax and bank fee structures can change. The model estimates what you should expect based on the inputs you provide. Always check the latest CBK auction prospectus before bidding, and consider speaking to a tax adviser about your specific situation.