Not the question you asked but are you in a position to switch your mortgage?
3% is relatively high in today's market and there are quiet a few options available at 1.95 - 2.4% depending on your circumstances.
Assuming that your LTV and LTI are good and you are in a financial position to switch, you could save a lot of money in addition making the lump sum payment. If the break fee is ~ €200 for €20k, then I'll assume it will be ~ €3k for your full €300k mortgage
Over the next 3 years, you will pay €27k in interest (€300k x 3% x 3yrs)
If you can switch to Avant at 1.95%, this figure becomes €17.5k. Plus the break fee (€3k) and some switching costs (€1.5k), you could comfortably save €5k over the next 3 years
Or if you can get AIB's 5 year green rates at 2.1/2.15%, the interest figure becomes ~€19k. Plus break fee of €3k and again you can save approximately €5k over the next 3 years. In this case, AIB offer €2k cashback to cancel out your switching costs
Definitely worth checking what rates are available to you here
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